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Dictionary of the History of Ideas

Studies of Selected Pivotal Ideas

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The term “man-machine” denotes the idea that the
total psychic life of the individual can be properly
described and explained as the product of his physical
organization viewed as a mechanical system in struc-
ture and function. An account of the ramified history
of the idea, however, requires a somewhat less rigid
definition, which will in several instances pertain to
the mechanization of only some, but not all, aspects
of mental activity; whereas on other occasions it must
be made broad enough to encompass the animal as well
as man. Similarly, the notion of “machine,” in particu-
lar when used as an equivalent of the living organism,
cannot be assigned in advance any precise or concrete
sense that would hold good over the entire length of
this study. The history of the man-machine is in large
part that of the relativity of the concept of mechanism,
as it has been understood with increasing breadth and
refinement, from Greek times to our own day, in those
sciences that have had a decisive influence on the
shaping and scope of the idea in question, namely,
physics, biology, medicine, technology, and (more re-
cently) chemistry and psychophysiology. Moreover, in
its relations to philosophy the fortunes of the man-
machine may be regarded as having closely conformed,
up to and since its first thoroughly consistent exposition
by La Mettrie in 1747, to the general curve followed
by the growth of materialism. However, it would be
historically sounder to eschew an absolute linkage
between the man-machine idea and any ultimate ma-
terialistic position of a metaphysical kind, despite the
strong affinities that persist logically between the two

The man-machine is typically a modern doctrine,
but it is necessary to go back to ancient Greece in


order to discover both the speculative tendency and
the positive elements from which it evolved. Quite
early in Greek thought the attempt was made to con-
ceive of the soul as an organized function of matter.
Some Pythagoreans spoke of it, for example, as the
“harmony of the body,” even if such a notion had for
them perhaps a more mystical than scientific meaning.
In Empedocles (ca. 490-30 B.C.), however, we already
find the rudiments of a psychology of sensation based
on exclusively physical factors. The external world,
viewed as continuous in substance with the organs of
sense, was described by him as registering replicas of
things (simulacra) directly on the senses in the form
of perceptions. This precocious empiricism, probably
indebted to the medical writings of Alcmeon, remained
tied to the error, prevalent in antiquity, that the heart
rather than the brain served as the sensorium commune.
There was, nevertheless, a glimmer of the man-machine
in the Empedoclean opinion that the varieties of psy-
chic constitution among men, including their different
aptitudes and characters, depend, as decreed by the
cardio-sensory theory, on the composition of their
blood, that is, on the size, distribution, and combination
of the particles assumed to compose it.

Epicureanism carried out to its conclusion, within
the technical limits imposed by Greek science, the type
of psychophysical explanation initiated by Empedocles,
and in so doing came nearest in the classical period
to the modern thesis of the man-machine. Because the
Epicurean tradition spanned several centuries, its
teachings underwent much change from the founding
of atomism in the fifth century by Democritus, through
its continuation under Epicurus (ca. 341-270 B.C.), to
the time of Lucretius (ca. 95-50 B.C.), in whose De
rerum natura
a synthetic presentation of its philosophy
has been preserved. As regards the atomistic prefigura-
tion of the man-machine, it will suffice to summarize
the Lucretian version. The soul, like all else in the
universe, was held to be a corporeal entity consisting
of an assemblage of atoms. Those atoms which made
up the soul, however, were of an extreme fineness
comparable to the intangibility and mobility of air
(pneuma), fire, or heat; in consequence they perme-
ated the whole body. Soul and body therefore remained
constantly in a state of mutual dependence by virtue
of physical contact. While the soul-atoms did not sepa-
rately possess life, consciousness, or sensibility, these
attributes of the organism were the outcome of their
appropriate combinations. From the Epicurean stand-
point, all psychic phenomena were envisaged as the
effects of specific (even if as yet ill-defined) atomic
structures. The operations of the various senses and the
faculty of sensation itself were explained on the same
basis. It was supposed that all objects emit semulacra
of themselves composed of a subtle grouping of atoms,
and that these replicas on entering through the related
sense-organs impinge upon the soul as sensations and
idea. It followed that the conscious and thinking prin-
ciple in man was mortal, and that the age-old belief
in personal survival after death was an illusion. The
soul temporarily forming with the body a composite
in which the role of each was essential to that of the
other, this reciprocity ended with the destruction of
the body and the dispersal of the soul-atoms. The
absolute material unity of man was thus affirmed—a
unity which made of death a simple physical event
in the cycle of aggregations, dissolutions, and re-aggre-
gations of the eternal atoms. The general picture of
man that emerged from Epicurean philosophy was that
of a momentarily coherent system of particles, of which
both the internal motions and the interactions with a
natural environment produced, by fundamentally me-
chanical means, not only the phenomena of life and
sensibility that were common also to animals, but the
higher mental functions believed to be peculiarly

Atomistic speculation contained within itself, at least
virtually, the seeds of modern science, including as an
offshoot of the latter the man-machine. When the
moment for the birth of that idea was to become ripe
many centuries later, the inspirations and precedents
offered by Epicureanism were to be put to important
use. But it must be admitted that ancient atomism itself
fell short of a genuine mechanistic conception of mind.
It was prevented primarily by its own abstract postu-
lates about the nature of matter from representing the
organism in terms of its observable structures and
processes. One detects still in the image of the soul
as a diffusion of atoms within the body something of
the earliest doctrines that identified the Greek pneuma
and the Latin anima with breath or air, in the naive
materialism typical of the origins of thought on the
subject. The persistence, however much transformed,
of such primordial intuitions in the Epicurean hypoth-
esis of ethereal soul-atoms, which served to exclude
in theory a truly physiological approach to the me-
chanics of vital and psychic phenomena, was a reflec-
tion, moreover, of the poverty of anatomical knowl-
edge in antiquity—a situation resulting from the
religious ban against dissections of the human body.
Not only was medicine of little help here, but what
existed as a science of mechanics in the same period
was also unable as yet to offer any schematization of
the laws of motion which might have led the Epicu-
reans to suppose that the organism was, rather than
a vague and fortuitous assemblage of atoms, an actual
machine of a definite type.

The handicap of inadequate scientific data was


compounded by the curious fact that classical atomism,
although it laid the foundations for the future of physi-
cal inquiry, remained itself singularly indifferent to the
objective truth or error of the particular theories it
framed about the “nature of things.” It failed to see
in its anticipation of the man-machine a starting point
of scientific study. The paramount aim of the atomistic
definition of soul, as of all Epicurean physics, was
ethical. In furtherance of this, what counted was the
type of explanation offered, rather than the detailed
form it took. The ethical aim of Epicurean physics
being to reassure its followers about the hazards of life,
this was believed best attainable by banishing from the
world the arbitrary intervention of the Gods. The
fatalistic belief in the soul's mortality was comforting
because death, or rather the punishments to follow
preached by religion, ceased thereby to be a source
of dread. To induce the ataraxia, or peace of mind,
of the sage, one atomistic theory, provided it was
credible, was obviously as good as another. Thus the
earliest approximation of the man-machine was taught
as an antidote for the superstitious terror of the super-
natural powers presumed to control human destiny. Its
antireligious emphasis accounts for the vigorous sup-
pression of the Epicurean idea of the man-machine,
along with the entire philosophy of which it was a
facet, once the official triumph of Christianity took
place; for the new faith was less tolerant of its critics
than many a paganism had been. The idea was not
to rise again to the surface and pursue its career until
the resurgence of pre-Christian modes of thought in
the seventeenth and eighteenth centuries. When that
was to happen, the underlying tension between religion
and the man-machine conception was also to be re-
vived, until the latter idea was to mature finally into
a full-fledged doctrine, a refutation of Christian dogma
about the spirituality and immortality of man's soul.

If Epicureanism supplied the materialist world view
that later nurtured the man-machine, it was from a
different source in Greek thought—from the Hippo-
cratic school and its descendants—that the specifically
medical background of the idea first came. The theory
of the four humors, which was to enjoy so durable a
vogue, attempted to explain the behavior of the mind,
particularly as manifested through personality-types,
in terms of physiological causes. Indebted, seemingly,
to the “four elements” of Empedocles and to the prev-
alent taste for microcosmic-macrocosmic analogies, the
treatise De natura hominis of the corpus Hippocrat-
dating probably from the second half of the fifth
century B.C., worked out a scheme of correlations
between the preponderance in the body of blood,
yellow bile, black bile, or phlegm, and the respective
predominance of the character-traits of sanguinity,
biliousness, melancholy, or apathy. Gross and fanciful
as this system of causes and effects was, the real value
of “humoralism” proved to be the scientific method
and medical philosophy it exemplified. By assuming
that mental states were regularly dependent on bodily
conditions, it made this dependency a crucial object
of further investigation and therapeutic practice. As
an adjunct to its humoral doctrine, the Hippocratic
school held also that climatological and other factors
in the natural environment acted upon the tempera-
ment by way of the body, thereby producing variations
of aptitude and mentality among individuals.

In the ultimate impact of ancient medicine on the
formation of the man-machine, the role of Galen
(129-ca. 199) was no less important than that of Hip-
pocrates. Not only did Galen organize the medical
knowledge of his day into a vast corpus, but his own
contributions to it were such as to strengthen notably
the link between humoralism and an incipient man-
machine attitude. While retaining and developing the
theory of the four temperaments and their related
psychic classifications, he laid the groundwork for a
physiology of the nervous system by being the first to
demonstrate experimentally that the brain was the
point of origin of the multitude of nerves which con-
trolled, by specific functions, the various vital, sensory,
or motor activities of the body. To explain how this
control was effected physically, Galen launched on its
long and adventurous career the hypothesis of “animal
spirits” composed of that invisibly rarefied fluid sup-
posed to be contained in the imagined tube-like hollow
of the nerves. Man was seen, consequently, as an orga-
nism regulated in its operations by a definite organ,
the brain, which, thanks to the animal-spirits of the
nervous network, mechanically received sensory mes-
sages from all parts of the body and sent back its
voluntary or involuntary commands. In this Galenic
model, of which the combined humoral and neuro-
logical aspects tend to construe man as a sort of hy-
draulic-pneumatic machine (reflecting in Greco-Roman
times the privileged status of water-technology and the
popularity of the pneuma-concept of soul), we have
already the rudimentary structure that in fact unifies
body and mind into an organic entity. On the basis
of it, Galenism foreshadowed a materialistic picture
of man, even though the philosophical opinions of its
founder remained eclectic and, on the particular prob-
lem of the soul, loyal to Platonic and Aristotelian
assertions of its substantial immateriality. But the soul,
in so far as it came under the double dominion of the
humors and the brain, was no longer treated as an
independent being, but rather as something so fatefully
bound up with the body that medical science was held
to be the most effective means of regulating the pas-


sions, and thereby of remedying character-disorders.
By proclaiming the interdependence of corporeal,
moral, and mental states in the interests of a thera-
peutic ideal, Galenic teaching approached the thresh-
old of the man-machine idea during the classical era—a
fact that La Mettrie's l'Homme machine was going to
appreciate. It is important, furthermore, to recall that
the Hippocratic and Galenic traditions, in contrast to
the ideological suppression of Epicureanism, remained
in authority without interruption until the seventeenth
century, and were thus able historically to exert, at
the right moment, a maximum influence on the matur-
ing of the man-machine, at least to the extent that the
latter idea had major roots in medical thought.

It remains, finally, to relate how the man-machine
was prefigured in the achievements of ancient technol-
ogy; that is, to what degree the latter succeeded in
simulating animal or human behavior by mechanical
means. The inventiveness of antiquity was applied, on
the whole, to machines for lifting or pulling heavy
weights (pulleys, winches, cranes, levers), engines of
war (catapults, siege and defense equipment), pneu-
matic and hydraulic contrivances (waterclocks, foun-
tains, pumps, water-organs), presses of various kinds,
and similar instruments of relatively simple design and
operation. Truly automatic devices were rare and,
when encountered, belonged mostly to the class of toys
and other objects intended for amusement or enter-
tainment, rather than to that of machinery for useful
work. Among the reports of such gadgetry that have
come down to us, surely the most remarkable deals
with the “automatic theatre” of Heron of Alexandria
(second half of the first century A.D.), who was perhaps
the most versatile mechanist of the Greco-Roman pe-
riod. The theater in question, as described in his treatise
Peri Automatopoietikes, featured a five-act tragedy
based on the legend of Nauplius; it was performed with
the appropriate dramatis personae, scenery changes,
sound effects, etc., all of it automatically controlled
by a system of strings, reels, cogs, and levers attached
to a motor consisting of a counterweight that de-
scended slowly and uniformly. The technological vir-
tuosity of Heron of Alexandria apparently did not,
however, have any philosophical meaning for his con-
temporaries. It may, for one thing, be said to have
come too late, when the gift for original speculation
had largely spent itself. But in a broader sense, the
triumphs of Greek engineering attributed to such
figures as Ctesibios, Philo of Byzantium, and Heron
remained outside the main stream of science. Even the
genius of Archimedes (d. 222 B.C.), whose generaliza-
tion of certain laws concerning the equilibrium of
bodies had intimated the modern synthesis of geometry
and physics, proved to be an isolated case, and failed
to inspire the following that his methodology deserved.
Because the Greek imagination in science was typically
theoretical in temper rather than given to contriving
machinery, there was something abortive, or at least
markedly premature, in the discoveries of an Archi-
medes and in the inventions of a Heron of Alexandria,
each of whom exhibited in his way a strong techno-
mechanical bent.

To make clearer why “machinism” did not become
a philosophical perspective in antiquity, it should also
be stressed that the mechanical arts and everything
pertaining to them were regarded as inherently too
base for such a purpose. Philosophy, chiefly aristocratic
in outlook from its inception, was concerned primarily
with contemplative or ideal pursuits. Nor did the pas-
sion for mathematics in the Pythagorean and Platonic
schools favor, as it has in modern times, the fusion of
philosophical and technological modes of thought,
because as a rule the mathematicism of the Greeks
remained “pure.” Behind these attitudes it is evident
that there was in operation a pervasive sociological
factor, which would have rendered the man-machine
idea “unthinkable” even if (contrary to what was
actually true) all of its logical and technical compo-
nents had already been given. Mechanical devices fell
within the department of the artisan, many or most
of whom were, in fact, slaves. The introduction of
related concepts or criteria into philosophical thinking
would have signified to the Greek intellect its own
“enslavement”; for the unconscious equivalent of the
man-machine, had such an idea been somehow pro-
posed, would have been the slave himself, in the sense
that the slave was quite literally man reduced to a
machine. By the same token, it is not merely fortuitous
that the rise of the man-machine doctrine will coincide,
in the eighteenth century, with two causally connected
revolutions, the one technological, the other socio-

To summarize, the man-machine was principally
approached in classical thought from three different
but converging directions: that of atomistic materialism
and its extensions in biology and psychology; that of
medical psychophysiology, as best seen in the Hippo-
cratic and Galenic schools; and that of the technology
pertaining to automata. These three approaches had
not yet found, however, the synthesizing mind capable
of bringing them effectually together; for not only were
the materials made available by each of them still
insufficient to that end, but the sociocultural climate
(which participates in the shaping of even the most
abstract notions) was such as still to exclude the possi-
bility of man's self-image as a machine.

The man-machine idea remained in abeyance during
the period of almost twelve hundred years when the


reigning Christian ideology checked or suppressed
whatever in the philosophical heritage of the past
remained unassimilable to its own position. The
mechanistic conception of human nature was, of
course, incompatible with theological dogmas affirming
the spirituality and immortality of the soul and pictur-
ing man as a creature of God endowed with free will.
It was not until the sixteenth century, when long
repudiated aspects of Greek thought were revived, that
a naturalistic view of man was reinstated. This first
resulted at Padua from the reinterpretation of Aristotle.
Reappraising from a medical standpoint Aristotle's
texts in the original, the Paduan criticism, especially
Pomponazzi's and Zabarella's, had the double effect
of rendering the spiritual permanence of the soul
undemonstrable by reason, and of redefining the facul-
ties of the “sensitive” and “intellective” soul as func-
tions of the “material form” of the body. The work
of Pomponazzi shows that Aristotelian metaphysics had
the potential of yielding an essentially naturalistic
psychology, to the extent that its key-concept of form
could be made to coincide with the structure itself of
the organism, that is, with anatomical and physiological
data. That such a development was at least a possibility
in the career of the man-machine idea is attested by
the fact that, when La Mettrie's Histoire naturelle de
(1745), inspired by medical materialism, gave a
preliminary theory of man, it did so in the context of
a scholastic metaphysics suitably construed for the
purpose. Nevertheless, the role of Peripateticism in the
evolution of the man-machine remained quite modest.
The reason was not only that Italian naturalism had
relatively little impact beyond the Alps, but also that
the imminent revolution in science stemming from the
physico-mathematical method was soon to be consum-
mated against, and stubbornly resisted by, those claim-
ing to be faithful to Aristotle. Therefore, a new and
opposing philosophy, meant to legitimatize a physics
concerned with formulating quantitatively the observ-
able laws of motion, would henceforth serve as the
conceptual framework for the man-machine. The
mechanization of nature, which found its most system-
atic and far-reaching rationale in Cartesian thought,
was the decisive step in the intellectual process that
led finally to the mechanization of man himself.

That process, however, was strongly helped by sev-
eral events in science and technology during the six-
teenth and early seventeenth centuries. Among the
most important was the rebirth of anatomy, particu-
larly under the impetus of Vesalius' epoch-making De
humani corporis fabrica
(1543). The modern mind
thereby became familiarized with the image of the
human body as a neat and exact assemblage of related
structures—an image made all the more incisive by
progress in the techniques of anatomical repre-
sentation. Thus the inevitable analogy between the
internal organization of the body and that of, say, a
clock was first a common fact of visual experience.
Harvey's discovery of the circulation of the blood (ca.
1616) was another occurrence of the same type. It
furnished the missing key to the dynamics of what now
appeared more than ever to be a hydraulic machine:
the organism was not only arranged like a clock, but
it “ticked” like one, with its mainspring simply a pump.
The task which thereafter devolved on physiology was
to explain, consistently with the mechanics of circula-
tion, the subordinate mechanisms of muscular move-
ment and of sensory as well as motor impulses. To these
permutations in man's self-perception should be added
the emergence of a technological ideal no less revolu-
tionary than the rest, already heralded before 1500 by
the remarkable vision of Leonardo da Vinci. The
resolve to conquer nature and make it serve man—a
theme that Bacon and Descartes soon elaborated phil-
osophically—was in time, along with the retreat of
occultist schemes of domination, to focus on the ma-
chine as the specific weapon of conquest. In the seven-
teenth century, it is true, the machine was still seen
as no more than a means to an end; there was no
question yet of a process of assimilation, technologi-
cally conditioned, between it and man. But the pas-
sionate use of a particular means modifies, in addition
to the end it serves, the agent whose destiny becomes
inseparable from its use. At the historic moment when
technological mastery of nature became a methodically
conscious goal, the idea of the man-machine was pre-
dictable by a general law of cultural change, according
to which man comes eventually to resemble the instru-
mentality of his ambition and power.

It was Descartes' definition of the animal as an
automaton that initiated the modern phase of the
man-machine. Although a similar opinion had been
voiced as early as 1554 by the Spanish physician
Gomez Pereira, it had no noticeable effect until it
reappeared as part of the Cartesian philosophical re-
form. French thought from Descartes to the Enlight-
enment thereby became the theater in which the con-
cept of automatism was by degrees generalized from
the animal to man. The bête machine doctrine had
resulted from Descartes' metaphysical dualism. Once
given the sharp distinction between a thinking and
extended being (res cogitans and res extensa), it was
patently less absurd to banish animals collectively from
the realm of thinking substance than to have to distrib-
ute “rational souls” to them from the ape down to the
flea. But more than a case of metaphysical expediency,
the animal-automaton served also to illustrate posi-
tively the universal mechanism of matter. As the bio-


logical counterpart of Cartesian physics, it was a theo-
retical culmination of the iatromechanical current
which had already become widespread in the medical
sciences of the first half of the seventeenth century.
The meaning of the beast-machine as a physiological
postulate can best be understood by viewing it in the
light of its human equivalent sketched in the Traité
de l'homme,
where Descartes, as if momentarily for-
getting his dualist position, seemed on the verge of
recognizing in man, too, an automaton. Historically,
the bête machine proved to be (contrary, no doubt,
to what its author intended) simply a minimal and
preliminary version of human automatism. In the long
run the animal acted as a mediator between the ma-
chine and man—a service which early attested the
projection from animal to human nature that has since
become a commonplace of biological and psycholog-
ical research. That the mechanistic emphasis of
Descartes' physiology threatened to undermine his
metaphysics by inviting a transformation of the beast-
machine into the man-machine, can be seen clearly
from the description of organic functions given in the
Traité de l'homme (1664):

... all the operations which I have attributed to this Ma-
chine, such as the digesting of food, the beating of the heart
and arteries, nourishment and growth, respiration, waking,
and sleeping; the reception of light, sounds, odors, tastes,
warmth, and other like qualities into the exterior organs
of sensation; the impression of the corresponding ideas upon
a common sensorium and on the imagination; the retention
or imprint of these ideas in the Memory; the internal move-
ments of the Appetites and Passions; and finally, the external
motions of all the members of the body... I wish that
you would consider all of these as following altogether
naturally in this Machine from the disposition of its organs
alone, neither more nor less than do the movements of a
clock or other automaton from that of its counterweights
and wheels...

(Oeuvres, Pléiade ed. [1953], p. 873).

The above passage shows that the technological
models with which Descartes equated the “organic
machine” were of a rather inept sort. The clock (which
Aquinas had long ago compared to the motions pro-
duced in animals by instinct and appetite) was to
remain, nevertheless, the seventeenth century's favorite
example of an automatic device simulating intelli-
gence. Descartes had in mind also analogies offered
by the hydraulically operated automata in the royal
gardens of Saint-Germain, which the Traité de l'homme
alluded to in order to explain how sense-perceptions
activate the brain:

External objects which... determine [the corporeal ma-
chine] to move in various ways according to how the
parts of the brain are disposed, are like strangers who, on
entering some of the grottos where those fountains are
found, themselves cause without being aware of it the
movements that take place before their eyes: for they cannot
enter without stepping on paving stones so arranged that,
for instance, if they approach a bathing Diana, they will
cause her to hide behind some shrubbery; and if they at-
tempt to pursue her, they will cause to come towards them
a Neptune brandishing his trident...

(ibid., pp. 814-15).

There is evidence that Descartes, seeking experimental
proof of his automatist doctrine, designed a little robot
that could perform somersaults on a tightrope. Al-
though such examples might well suggest that his sense
of the imitative powers of mechanism was naively
exaggerated, it is unlikely that Descartes regarded
clock-like automata as reproducing in a literal fashion
the far more complex and versatile behavior of animals.
Ultimately, his notion of the beast-automaton was de-
duced from the general mechanism of nature, while the
actual models proffered in support of it were merely
the best that the technology of the period could provide.
Cartesian biology pictured the living organism—
not unlike the universe of whirling vortices (tourbillons)
which enclosed it—as basically a hydraulic machine.
The activity of the nervous system, patterned on that
of the vascular circulation, was explained by supposing
that the nerves contained a rarefied fluid—i.e., the
animal spirits (Esprits animaux), made up of the finest
blood-particles—which, propelling itself back and
forth between the brain and the periphery of the body,
controlled all sensory and motor functions. To this
hydraulic scheme Descartes added a thermodynamic
feature by assuming that the heart operated on heat;
and also, as his most promising contribution, he
imagined a primitive form of reflex mechanism to
account for involuntary muscular movement.

The modern idea of the man-machine came into
being largely as a result of the development that the
animal-machine and the physiological science related
to it underwent in common. The final outcome had
indeed been foreseen in Descartes' own time, and gave
rise to objections against his view by various critics,
some of whom went so far as to accuse him of heresy
and of abetting materialism. In the “Sixth Objection”
to the Méditations métaphysiques, a group of theolo-
gians claimed that the beast-automaton would lead its
supporters to conclude that the continuity in intelli-
gence between animals and human beings was attribu-
table simply to machines of differing levels of com-
plexity. This rejoinder was repeated often by opponents
of the bête machine, who thereby unintentionally
bestowed a measure of popularity, and even plausibil-
ity, on the very inference that they were eager to avert.

The problem of “animal soul” became the subject of
endless controversy, lasting well into the next century,
between Cartesians and anti-Cartesians. While in one


sense such metaphysical polemics for or against the
animal-machine could only have proved futile (for it
is impossible to know if any creature other than man
is endowed with what we experience inwardly as res
), in another sense it helped indirectly to render
the automatist thesis more acceptable. This came about
in several ways. Those who sought to refute Descartes
on the grounds that beasts often exhibit, by their skill
and cunning, a degree of intelligence equal and occa-
sionally superior to that of human beings, were in effect
citing evidence that could boomerang against them.
For when the man-machine philosophy was at last
proclaimed, its exponents—with La Mettrie at their
head—could argue that if animals, despite their alleged
merits, were mere machines, there remained no reason
to suppose that human abilities implied a loftier kind
of causation. The adversaries of the Cartesian doctrine,
relying on scholastic tradition, also proposed a “cor-
poreal soul,” situated midway between materiality and
spirituality, as the specific principle of feeling and
intelligence in animals. But the notion of “corporeal
soul,” a derivative of the Aristotelian “substantial
forms,” was logically inconsistent, and in the end,
encouraged some to identify it more conveniently with
the organic machine itself. That, at any rate, was what
La Mettrie did in his Histoire naturelle de l'âme, in
which Peripateticism, with reminiscences (as noted) of
Pomponazzi and the Paduan school, became an ingre-
dient of the materialistic definition of soul. Those
Cartesians, moreover, who took up the cudgels for the
bête machine were obliged to explain, in ever more
ingenious detail, how merely mechanical processes
could be the source of all the amazing variety of animal
actions. In so doing, they freely introduced Descartes'
principles of psychophysiology into the subject of ani-
mal automatism, with the result that the mechanistic
interpretation of psychological phenomena, at least in
animals if not yet in man, crystallized as a general

To the above developments should be added the
curious vogue that the beast-machine enjoyed in cer-
tain religious circles, especially among the Jansenists.
Far from regarding it as heretical, the latter, repre-
sented by their leading thinker, Arnauld, were fasci-
nated by the automatist concept, discovering in it (as
Descartes had intimated) a number of theological ad-
vantages. Not only did it set in a brighter light the
dogma of a separate and transcendent destiny for the
human soul, but it absolved men (and God) of blame
for the sufferings erroneously believed to be inflicted
on innocent beasts. More important still, it attested to
the infinite art and wisdom of God, who had contrived
such marvelous automata capable of imitating intelli-
gent behavior. This excursion of the animal-machine
into the sphere of natural theology was, in particular,
to offer a dubious precedent which played eventually
into the hands of the free-thinkers. For it followed that,
if God could create such remarkable automata as ani-
mals were acknowledged to be, there was no need for
him to do anything more, in creating man, than to
improve on the mechanical models already in exist-
ence. The man-machine idea will thus ironically find
theological support in the assertion that it is impious
to consider the Supreme Artisan incapable of fashion-
ing a machine as complicated and as admirable as man.

Although the animal-soul debate was concerned
mainly with the question whether beasts were or were
not pure automata devoid of feeling and thought,
Descartes' own position had in reality been more
nuanced and even somewhat ambiguous. In denying
a soul to animals, he had meant only that they were
without rational awareness—an opinion confirmed
empirically both by the “unreflecting” efficiency of
their actions and by their lack of the linguistic means
needed for the formation of abstract ideas. This sig-
nified that the animal, unlike Descartes, did not per-
form intellectual operations of the type cogito, ergo
but its inability to cogitate did not necessarily
deprive it also of all nonreflective kinds of mental
activity, such as simple consciousness, memory, emo-
tion, and perception. Descartes conceded to the beast,
in fact, a level of psychic life directly dependent on
its physical organization. The extension of the bête
doctrine, so understood, to the behavior of
man by those Cartesians, prone to naturalism, who saw
in it above all the opportunity to explain psychological
phenomena mechanistically, had its initial logic in
Descartes' over-restrictive definition of the soul as a
purely rational substance distinct from all else in the
universal mechanism where it was so tenuously lodged.
The proposal to investigate within the machinist con-
text, first in the animal and subsequently in man, such
“sub-rational” faculties as sensation, memory, imagi-
nation, feeling, and volition, oriented the future pro-
gram of psychophysiological science and thereby set
the stage for the maturing of the man-machine idea.

Among those who notably caused Cartesian thought
to evolve in this direction, Henricus Regius, professor
of Medicine at Utrecht, gave to the automatist thesis,
in his Fundamenta physices (1646), an interpretation
which, neglecting dualist metaphysics, stressed the
conformity of psychic processes with their organic
counterparts. Jacques Rohault's Entretiens sur la philos-
(1671) followed Descartes in denying to animals
a rational soul, but thereupon proceeded to examine
the remaining aspects of their conscious life in terms
of those mechanical structures assumed to be the basis
of the vitality and sensibility which they manifested.


In a similar exposition of the bête machine, Pierre
Sylvain Régis (Système de philosophie, 1690) had as his
purpose not so much to deprive animals of attributes
commonly included under the designation of their
“soul,” as to demonstrate that those same attributes
were owing to “the arrangements of their organic parts
alone, and to the heat of their blood and the force
of their animal-spirits.” In this physiologizing inherit-
ance of Cartesian natural science, the animal-spirits in
particular were soon to have a privileged role, namely,
as the innervating substance believed to engender and
sustain the higher functions of the brain. Some ad-
vanced thinkers all but substituted this substance for
the soul itself.

Thus the progress of physiology tended to minimize
the “ghost” which Descartes had found it metaphysi-
cally necessary to introduce into the “human machine”
of the Traité de l'homme. An inherent contradiction
of dualism had been the supposed interaction between
a substance that occupied—indeed was—space and a
substance—thought—that was essentially nonspatial.
Given the impossibility of discovering the laws of such
an interaction, there could be no science of the cause-
and-effect relations between body and mind in accord-
ance with Cartesian principles. Descartes' own attempt
to solve the problem by assuming that the soul was
housed in the pineal gland, where it acted like a brake-
man switching the incoming impulses of the animal-
spirits in one direction or another, can only be consid-
ered futile in view of both the neurological fantasy
and logical inconsistency that it displayed. Indeed,
dualistic psychology led into a blind alley. The at-
tempts of Leibniz, Malebranche, and Spinoza—each
of whom was concerned to overcome within the
framework of dualism the dilemma posed by Descartes'
unintelligible parallelism of mental and bodily func-
tions—did not in the end forestall the solution of the
dilemma that was forthcoming from the man-machine
philosophy. If Leibniz' pre-established harmony,
Malebranche's occasionalism, and Spinoza's monism
vindicated, each in its way, a metaphysical modality
of the mind-body correspondence, none of these ex-
planations was of any special use in determining em-
pirically the laws which governed that correspondence.

As it turned out, the impasse of dualism seemed to
be circumvented best by the increase in knowledge
of the central nervous system, and particularly of the
cerebral localization of specific functions. The result
of such advances in physiology (which by La Mettrie's
time had arrived at a rough differentiation of the types
of activity peculiar to the cortex, cerebellum, and
brain-stem, as well as at the stage of a comparative
neuro-anatomy of man and several animal species), was
the gradual replacement of the unlocatable soul by the
brain itself, which came to be seen as a “machine”
producing thought. The long-run sterility of dualism
as a psychological hypothesis—for it could only lead
either to a gratuitous dichotomization of its human
subject, or to the introduction of a nonfunctional soul
into the unity of body and mind—caused it at length
to be abandoned by certain unorthodox thinkers in
favor of the man-machine hypothesis, which by con-
trast had the advantage of recognizing the concrete
nature of man as that of a being in whom mental and
physical events were never divorced from one another.

The triumph of mechanistic psychology cannot be
understood, however, without taking fully into account
the influences exerted on it, often in an eclectic man-
ner, by the overlapping currents of Hobbism, Lockean
empiricism, and Epicureanism in the intellectual set-
ting of the early eighteenth century. In the De homine
(1658) of Hobbes, there was already outlined, contem-
poraneously with the Cartesian postulate of automatism,
a complete rationale for the mechanization of mind.
Inspired by the new physics, Hobbes was the first to
reduce all things to nothing but bodies in motion; and
since for him only efficient causes were real, psychol-
ogy and epistemology became branches of mechanics
like any other science of nature, except that imper-
ceptibly minute motions were said to be involved in
the entry of sense-impressions into the brain. Psychic
phenomena were thus conceived essentially as “a mo-
tion in the internal substance of the head.” The gross-
ness of Hobbesian materialism, coupled with the anti-
experimental and deductive method that supported it,
limited somewhat the historical importance of its
precocious version of the man-machine theme. While
there was no hesitancy on its author's part to describe
man abstractly as a machine, the scientific motive for
imagining specific analogies between mechanism and
organism was lacking in Hobbes' reliance on physico-
mathematical generalities. Nevertheless, his contri-
bution was valuable especially because of the linkage
it effected between the mechanics of sensation and an
empirical theory of knowledge. In following to its
conclusion this epistemological lead, the materialists
of the Enlightenment will succeed in “mechanizing”
the homo duplex of metaphysical tradition. The imme-
diate ground of this final step, however, proved to be
the empiricism of Locke, who far more than Hobbes
shaped their thinking. Once the procedure to refer
mental and emotive states to the organic dispositions
that accompanied them had become well established,
it seemed logically and psychologically appropriate to
combine this unification with a consistent sensa-
tionalism. Approaching Lockean epistemology with a
marked materialistic bias, La Mettrie and those who
followed him achieved between empiricism and mech-


anistic biology a synthesis which eliminated all recourse
to an immaterial principle in analyzing how the mind
acquires its ideas.

In this outcome, the role of Gassendi, who cham-
pioned an empiricism of Epicurean stamp, paralleled
and soon merged with that of Locke. Moreover,
Gassendi's revival of the atomistic definition of sensi-
tive soul as a rarefied, fiery substance was easily assimi-
lated to the mechanistic physiology then prevalent,
serving to reinforce the opinion that psychic activity
resulted from the flow of Esprits animaux back and
forth between the brain and the sensory apparatus.
Such a combination of automatism, atomism, and
empiricism is well seen in the case of Guillaume Lamy,
a professor of the Paris Medical Faculty, who as early
as 1678 anticipated the man-machine in his Explication
mécanique et physique des fonctions de l'âme sensitive,
ou des sens, des passions et du mouvement volontaire.

But in the trend to materialism which thus drew
sustenance from a broad spectrum of sources, the im-
portance of Spinoza as a catalyzing agent should not
be neglected. It was mainly in Spinozism that La
Mettrie and a number of philosophes found, as part
of what they took to be a naturalistic and atheistic
metaphysics, the key notion of necessity which they
consolidated with the man-machine idea, arriving at
a doctrine of mental and moral determinism that made
of free-will a mere subjective illusion.

All the attitudes and influences discussed above made
their least inhibited appearance in the free-thinking
literature that circulated privately in France after
1700, and in which different approximations of the
man-machine may be said to have enjoyed at first an
“underground” existence. The idea was originally
propagated, therefore, as a salient feature of the radical
critiques aimed at the official ideology of the Ancien
In this initial phase of its career, the incipient
man-machine idea had predominantly an antireligious
and subversive meaning, and was regarded rightly, on
the whole, as dangerous to social and political institu-
tions by the defenders of tradition and authority, who
sought, though ineffectually, to suppress it. Among the
many examples of such a use of mechanistic psychology
are to be found the revolutionary Testament (1729) of
the notorious apostate priest, Jean Meslier, and, in the
class of anonymous works extant in manuscript, L'Ame
and Essai sur les facultés de l'âme.

It was not, however, until the publication of La
Mettrie's L'Homme machine (1747) that the idea pro-
vocatively epitomized by its title was at last affirmed
as the basis and focus of a coherent philosophical
position. From profusely cited evidence of what he
took to be an invariable correlation between mental
and physical states in the individual, La Mettrie con
cluded that, in addition to every vital and involuntary
function, all the forms of conscious life—such as sensa-
tion, the passions, memory, thinking, volition—are
regularly contingent upon the “organic machine,” and
more exactly on the structures and activity of the
central nervous system. Characteristic of this viewpoint
was the fact that its author, himself a physician who
had been a disciple of the leading iatromechanist,
Hermann Boerhaave (1668-1738), gave it as the gist
of a materialist philosophy that remained closely re-
sponsive to the methodology, scope, and aims of the
medical sciences. As a result, while his advocacy of
the man-machine still retained numerous antireligious,
polemical, or propagandist traits, it had the originality
of being put forward primarily as a general heuristic
hypothesis for the scientific study of behavior. La
Mettrie eschewed, as far as possible, its metaphysical
implications (whether positive or negative) in regard
to the ultimate nature of matter and mind, or of the
causality underlying their mechanistic union. He
thereby succeeded in harmonizing the experimentalist
ideal of modern science, which had only recently come
to the fore in France, with his main thesis. The man-
machine was held to be a logically valid notion not
because it expressed any apriorist truth about human
nature, but on the strength of induction from verifiable
psychophysical data. Consistently with this, La Mettrie
was fond of analogies that pictured the mind as a
“thinking and feeling machine” into which ideas,
entering as coded symbols, were not merely stored,
compared, and combined, but were also continuously
colored and modified by emotive and instinctual mes-
sages flowing into the same centers of perception. The
goal of psychology, according to the man-machine
hypothesis, became the gradual clarification in detail
of the complexities, admittedly limitless, of this cere-
bral process—a goal which, La Mettrie believed, held
out the best hope of diminishing the enigma that man
posed both generically and individually.

Although he stated that his doctrine was simply that
of the beast-machine drawn out to its final conse-
quences, actually La Mettrie's use of mechanism as a
biological concept represented an important advance
over the Cartesian view of the organism as essentially
like any man-made, artificially actuated device. In
contrast to such a “dead mechanism” approach, La
Mettrie sought to describe the vital machine with
which man was equated as a dynamical and self-suffi-
cient system typified by an internal finality. “The
human body,” he wrote, “is a machine that winds its
own springs—the living image of perpetual motion”;
and more organismically: “man is an assemblage of
springs that are activated reciprocally by one another,
without it being possible to say at what precise point


of this human circle nature has begun.” This concep-
tion was only in part inspired by technological
achievements. The favorite criterion of an “intelligent”
machine, in the eighteenth century as in the seven-
teenth, continued to be the ordinary clock, alongside
which La Mettrie placed, however, the harpsichord
as a model for the epistemological mechanics of regis-
tering, composing, and reproducing ideas like so many
musical notes played on the cerebral “chords.” Special
mention deserves to be made also of Vaucanson's auto-
mata, the most ingenious of the period, which had in
fact been contrived as practical simulations of different
biological processes. There was among others his fa-
mous “duck,” which could paddle itself about, and
“digest” food by means of a stomach that substituted,
as might be expected, mechanical for bio-chemical
operations. But while the homme machine clearly
profited from such scientific interests, it rested on more
specifically biological grounds. La Mettrie referred the
capability of automatic reactions which the organism
possessed to the reactive energy manifested in a con-
crete way by the key-phenomenon of irritability. He
thus saw in the property of muscle-tissue irritability,
which Haller had recently discovered and illustrated
experimentally, the vital force responsible for the
purposive dynamism peculiar to physiological, as com-
pared with merely physical, machines.

In most quarters, the man-machine philosophy was
angrily denounced as a dangerous paradox, first, be-
cause it offended peoples' religious sentiments or de-
flated their vanity (which La Mettrie fully intended);
but it was even more offensive because of certain
implied moral conclusions. Claiming in his Discours
sur le bonheur
(1750) that happiness was a mental state
dependent essentially on somatic conditions, La
Mettrie divorced the “supreme good” of man from the
practice of traditional virtues, and redefined it primar-
ily as a medical rather than an ethical question—a
reversal which, taken together with his readiness to
relieve even criminals of the “disease” of guilt and
remorse, struck his contemporaries as an immoralist's
cynical defense of vice and anarchy. The usefulness
of La Mettrie's deterministic—hence amoral—psy-
chology is, however, far plainer to us now than it was
to his own century. The man-machine idea had the
merit of bringing to the age-old problem of the moral
perfectibility of man a whole new dimension, consisting
in the ability of medicine to act upon the mind, emo-
tions, and personality by variously modifying their
underlying organic causes. La Mettrie may be said to
have introduced into the sphere of general ethics a set
of criteria inspired by medical humanitarianism, and
supported by the psychiatric evidence that man's be-
havior is not in fact as free as it is commonly held
to be.

Since La Mettrie, almost all materialist philosophy
has subscribed in one form or another to the man-
machine (even if the term itself, doubtless owing to
its shock value, has never been popular). The leading
advocate of the idea later in the eighteenth century
was Diderot, whose versatile genius provided a
nuanced and rich context for its development. He
brought out, especially, its organismic potential by
differentiating three structural levels in the human
machine—that is, the elementary “cellular” units, the
individual organs, and the organism as a whole—and
by placing at the apex of their integrated operations
the various manifestations of psychic life. Assuming,
furthermore, that there was in nature an indeterminate
number of “molecules,” endowed with latent sensi-
bility, which coalesced according to fixed laws, the
Rêve de D'Alembert (1769)—which would remain
unknown until the next century—sought to trace, with
a gift for mechanistic analogies that was as much liter-
ary as scientific, the emergence of life, consciousness,
sensation, the passions, memory, and reflection in terms
of the ascending complexity and functional continuity
of the related organic structures. More than this radical
morphologizing of the man-machine, Diderot was the
first to present the latter within the framework of a
general transformistic theory embracing the history of
all the animal species, with the outcome that man was
perceived not merely as a machine, but as one that
had been slowly constituted in time by the same uni-
versal laws of moving matter that governed his present
behavior. The man-machine thereby found a suitable
place in the system of evolutionary materialism that
Diderot expounded in a largely hypothetical and con-
jectural vein. It was in his work, moreover, that the
modern socioeconomic overtones of the idea first began
to appear, although still indirectly, alongside its far
more obvious antecedents in biological and medical
science. When seen in relation to the enormous impor-
tance that Diderot ascribed, in the Encyclopédie, to
the machinery and techniques of the manufacturing
arts, the man-machine idea would appear to have been
on the verge of a new significance. In his dual effort
to mechanize man and to humanize technology, there
was implicit a coextensiveness of the man-machine
with the nascent reality of an industrial world, in which
man was to be described at length not merely as himself
a machine, but as the creator and master of countless
other machines that would be objectifications of himself
and, as it were, his “offspring.” Diderot thus succeeded
in evoking the broader implications, both biological
and techno-social, of the man-machine; but no less
clairvoyant was his sense of the basic contradictions
between an impersonally mechanistic and deterministic
view of human nature and man's inward awareness of
freedom in choosing the moral, artistic, and affective


values essential to his experience. The probing treat-
ment, in a fictional work such as Jacques le fataliste,
of this dilemma posed by Diderot's equally deep
commitment to a humanistic and to a scientific vision
of things, served in the end to point up a permanent
paradox at the core of existence itself.

Among other versions or near-versions of the man-
machine in the fertile eighteenth-century milieu, the
physiological psychology of David Hartley should be
noted. Influenced by Newton's theory of the ether no
less than by Newton's reduction of the multiplicity of
physical events to a single principle, Hartley's Obser-
vations on Man
(1749) proposed to interpret all mental
phenomena as resulting from vibratory motions in the
brain and nerves—a hypothesis that had the great
advantage, in his eyes, of accounting for the mechanics
of the “law of association” by which all ideas were
assumed to cohere. Although his associationist psy-
chology, unlike the man-machine doctrine, preserved
a formal distinction and parallelism between body and
mind, Hartley did not hesitate to apply his vibration-
principle in a comprehensive and deterministic fashion;
he thereby represented the organism in general on the
model of an elastic machine in which the impact of
external events generated the specific vibratory re-
sponses that were the biological basis of every variety
of psychic event.

A different and more limited use of the man-machine
idea may be found in the two treatises of Helvétius:
De l'esprit (1758) and De l'homme (1774). Conceding
the premiss that “Man is a machine which, once set
in motion by physical sensibility, executes all its acts
necessarily,” Helvétius elaborated a rigidly environ-
mentalist theory of education by way of explaining the
enormous variations among individuals. The corrective
to this one-sided method came, however, with
Diderot's Réfutation d'Helvétius, in which it was
argued that a psychology aiming to be at once materi-
alistic and sensationistic must consider as a variable,
not only the total environment in which each mind
develops, but the organism that underlies and informs
its development.

In the writings of Holbach, the man-machine took
a militantly atheistic turn. His Système de la nature
(1770) made it the starting point of an intransigeant,
rather reductive materialism, which, beyond its vehe-
ment anticlericalism, had positive ethical and political
goals. The Holbachian man-machine served, more pre-
cisely, as the psychological complement of a “natural
morality” derived from the pleasure-principle and
consistent with the rule of social utility. This he op-
posed sharply to the “unnatural,” spiritualist morality
imposed by the Christian religion, and called for a
radical reform of the political institutions of the Ancien
in the name of the felicity to which man, as
a physical being, was logically entitled in this world.

Finally, in the major contribution of Cabanis, Rap-
ports du physique et du moral de l'homme
(1795), the
culmination of eighteenth-century interest in psycho-
physiology may be witnessed. Convinced no less than
La Mettrie, Diderot, or Holbach of the primacy of the
organic machine, he combined this approach in extenso
with the method by which Condillac and Helvétius
had already furnished a descriptive analysis of the role
of sense-perception in the formation of ideas. In a
well-known passage, Cabanis pictured the brain as an
organ that produced thinking in the same manner that
the stomach digested food, adding: “We conclude that
the brain somehow digests sense-impressions, that it
effects organically the secretion of thought.” Contrary
to this rather blunt formula, he worked out the details
of his psychophysiology in a methodical and thorough
way, laying special stress on such factors as age, sex,
temperament, diet, physical exertion, occupational
pursuits, pathological conditions, the use of drugs and
stimulants, climate, and so forth. As in La Mettrie, the
theme of “physiological salvation” loomed large,
supported by the broad responsibility that Cabanis
granted to medical science in the improvement of the
human personality. On the other hand, it must be
admitted that Cabanis referred only summarily to the
actual mechanistic character of the organism, and, if
anything, chose to play down the man-machine equa-
tion during the post-Revolutionary years when it was
linked in public opinion with the ideological excesses
that atheistic materialism was accused of having pro-

In retrospect, the career of the man-machine idea
during the Enlightenment may be said to have con-
sisted of two phases. Up to about 1740, the concept
of mechanism with which physiologists remained
imbued was too rigid and narrow to offer, except in
isolated instances, plausible models for the organic
behavior it pretended to interpret. Beginning with
the 1740's, however, a profound shift took place in
biological speculation, exemplified by such figures as
Buffon, La Mettrie, Diderot, and Maupertuis, the effect
of which was to bring into sharp focus precisely those
qualities of living things that would strike later gener-
ations as vitalistic rather than mechanistic in character.
This reorientation of interest did not, as might have
been expected, bring about the rejection of the estab-
lished modes of explanation; instead it resulted in a
new tendency to conceive of the mechanical with a
degree of flexibility and imaginativeness sufficiently
great to allow the inclusion of vital phenomena within
the compass of loosely mechanistic hypotheses. To be
sure, the notion of mechanism, in such a stretching of
definitions, no longer corresponded to the rigorously
geometrical method of the Cartesian school. By a


seemingly paradoxical, but in reality merely transi-
tional step, the mechanistic biology of the second half
of the eighteenth century ceased to be mathematical
in spirit, and even sought to transcend, with an attitude
of deliberate antimathematicism on the part of Diderot
and Buffon, the authority of classical mechanics, which
was now felt to be, however philosophically valid,
futile and stifling in a technical sense. Inevitably, the
commitment to mechanistic principles or models
among such biological-minded philosophes as La
Mettrie and Diderot had something vague and sup-
positional about it; what it gained in suggestive visual
power, it lost (at least temporarily) in analytical clarity
and quantitative precision. The truth is that the century
which invented the man-machine disposed as yet of
very modest means for inferring biological, to say
nothing of mental, processes from what was reliably
known about the behavior of the inanimate world. The
meaning of the man-machine idea, as propounded by
La Mettrie or Diderot, was therefore above all an
affirmation of scientific faith—an appeal addressed to
posterity—concerning the ultimate fecundity of the
mechanistic method in bridging the gap between the
living and nonliving, and between the conscious and
unconscious, aspects of a presumably unitary nature.

It was in the Enlightenment that the man-machine
idea may be said to have attained optimum expression,
aided by the pre-Revolutionary thrust of materialistic
and atheistic attitudes. But even then its success ex-
tended only feebly beyond the borders of France to
countries such as England and Germany, where intel-
lectual loyalties remained conservative. In the first half
of the nineteenth century, moreover, the vogue of
idealistic philosophy and introspective psychology,
under the sway of romanticism, forced a broad retreat
of the man-machine thesis. From this temporary eclipse
the latter will gradually work its way up again to a
new kind of prominence by the end of the century,
under the influence of scientific developments favora-
ble to it. Despite its final vindication, the man-machine
will never quite regain its past authority as a systematic
principle. It has survived since the eighteenth century
mainly as an essential element—or often as a basic
tendency—present either explicitly or implicitly in
various configurations of thought in those disciplines
that have contributed most to its growth. Owing to
this changed historical status of the question, it would
seem unprofitable henceforth to treat the man-machine
idea sequentially. Rather, its fortunes will be assessed
in relation to pertinent progress in the fields of biology,
physiology, psychology, technology, and philosophy.
Such a procedure is all the more fitting because of the
differentiation that the sciences themselves underwent
during the nineteenth century in the course of their
emancipation from “natural” and “mental” (or
“moral”) philosophy. Following this specialization
of the methods and goals of research, the man-machine
came to have significantly different applications and
meanings for each of the branches of knowledge in
which it enjoyed a vested interest.

The advances in neurology proved specially germane
to the resurgence of the idea. Charles Bell's (1774-
1842) discovery of the dual character of the nervous
system served to clarify the distinction between
efferent and afferent impulses, thus preparing the
ground for a comprehensive and exact investigation
of reflex action. The work of Claude Bernard (1813-78)
on vascular reflexes and on the regulatory role of the
sympathetic system was a forward stride for the man-
machine, because it showed experimentally that the
viscera, by direct or indirect links to the brain, were
able to produce bodily changes affecting memory,
perception, emotivity, and thinking. In fact, the gen-
eral elucidation since the early nineteenth century of
the varieties of reflex mechanism, together with the
more recent extension of the principle to the Pavlovian
conditioned reflex, has demonstrated in detail how
far specific forms of conscious activity proceed from
the integrated automatic play of the nervous apparatus.
The perfecting of “neuron theory” led simultaneously
to a better understanding of the nature of neural con-
duction and of psychophysical dynamics. To these
discoveries should be added, of course, the accumula-
tion of data concerning the problem of cerebral local-
ization. From the pseudoscientific “cranioscopy” of
Franz Joseph Gall (1758-1828), through the crucial
researches of Pierre Flourens (1794-1867) on the be-
havior of decorticated pigeons, to the tentative brain-
topography sketched from clinical observation of vari-
ous motor and sensory types of aphasia, the nineteenth
century offered increasing evidence for the belief that
the central nervous system was the adequate and con-
trolling instrument of mental life. Such a conclusion
was supported, moreover, by what histological analysis
revealed in regard to the association-patterns of fibres
and the functional stratification within the brain.

Nineteenth-century philosophy mirrored or con-
firmed, albeit in a minor key, the standpoint of human
machinism. It was favored by Comtean thought to the
extent that the latter insisted, as against introspective
or speculative approaches, on the value of a positivistic
method in psychology which, in the historically given
circumstances, could only lead to the primacy of the
physiological factor. The current of materialism that
came to the fore in Germany around the mid-century,
represented by figures such as Feuerbach, Vogt,
Moleschott, Czolbe, and Büchner, took for granted the
validity of the man-machine conception. In England,


Spencer's “Synthetic Philosophy,” although not
actually materialistic, did not hesitate to classify
“mental science” as one of the natural sciences, with
the result that in the Spencerian hierarchy of the sci-
ences, psychology mediated the transition from biology
to sociology. G. H. Lewes (1817-78), rejecting the
dualist separation of mind and body, held that “sen-
tience” was a mechanical process peculiar to animate
beings, out of which, under the appropriate conditions,
consciousness in all its degrees developed. Hippolyte
Taine (1828-93), who was inclined to view man as a
“nervous machine” and to define thoughts and feelings
deterministically as products not unlike sugar and
vitriol, applied his psychophysical theories to literary
criticism; while, under his aegis, Émile Zola and the
naturalists sought to illustrate through the medium of
fiction that individual fate was the inexorable outcome
of hereditary and environmental forces.

Physiological psychology as a special branch of sci-
ence flourished under the stimulus of the aforemen-
tioned interests. In the period roughly from 1830 to
1860, the group of German experimentalists which
included J. Müller, Virchow, Helmholtz, Du Bois-
Reymond, and others, made remarkable progress in the
study of the physiology of sensation and perception.
Rudolph Hermann Lotze's (1817-81) Medizinische
Psychologie, oder Physiologie der Seele
(1852), a proto-
type of many similar treatises, was proof that the
viability of the man-machine idea did not narrowly
suppose monistic or materialistic convictions; for its
author, although a philosophical idealist and occa-
sionalist, regarded the nervous system as a pure mech-
anism in his discussion of it as the basis of mind. A.
Horwicz (Psychologische Analysen auf physiologischer
1872-78) studied emotion as the somat-
ically conditioned source of consciousness and of psy-
chic life in general. T. Ziehen's Leitfaden der physio-
logischen Psychologie
(1891) affirmed, among other
things, that there was no real distinction between vol-
untary and involuntary thinking, thus echoing the
automatist theory propagated by the eighteenth-
century materialists. These principles were expanded
upon by H. Münsterberg (Grundzüge der Psychologie,
1900), who predicted that psychology would become
an exact science only in so far as it utilized the un-
equivocal evidence furnished by neurophysiology. In
England, too, there was a parallel tendency to explain
the energetics and conduct of the mind in terms of
its organic constituents, as attested by the work of A.
Bain (The Senses and the Intellect, 1855) and by that
of such exponents of the same school of psychology
as T. Laycock (Mind and Brain, 1860), W. B. Carpenter
(Principles of Mental Physiology, 1874), and Henry
Maudsley, who plainly took the view (in Physiology
and Pathology of the Mind,
1867) that consciousness
was a by-product of brain processes. In America,
William James gave a large place to the physiological
method in his investigation of behavior, as best seen
perhaps in the James-Lange theory of emotion.

A decisive factor in the long-run success of human
machinism was Darwinian biology and the new orien-
tations that it provoked in psychology. The hypothesis
that man was descended from lower forms of life
dramatically weakened whatever presumption was still
left that his origins and nature had a spiritual, tran-
scendent dimension; and in the same proportion it
reinforced the axiom that all human characteristics
were natural phenomena admitting of natural explana-
tions. It was consistent with evolutionist logic to ex-
plain the diverse levels of psychic capability in man
as direct correlates of the ascending order of complex-
ity and differentiation that the selective struggle for
existence had wrought in his organic endowment. The
continuity thus established between him and the higher
animal species was an invitation to study human beings
by the same behavioral criteria, rooted in biologically
given instincts and needs, that were appropriate (and
indeed inevitable) in the study of animals.

The combined impetus of the developments in sci-
ence and philosophy that have been briefly summarized
was responsible for the reemergence of the man-
machine doctrine at the start of the twentieth century
with the sort of intellectual respectability that it had
clearly lacked in its eighteenth-century version. Its
restored vitality involved, of course, several qualifica-
tions of its meaning and scope. The new man-machine
did not signify any simple or self-apparent equation
between human nature and man-made mechanical
devices 9a fact which indicates why the idea itself
caught on much better than La Mettrie's rather offen-
sive sounding name for it). On the contrary, the ma-
chinery of the body was now seen as an enormously
complex self-adaptive system of a physicochemical
type analyzable into molecular structures, for which,
moreover, no faithful analogue could be cited among
artificial machines. The man-machine therefore
affirmed only that the dynamics of organism must
ultimately be governed by the same laws that governed
mechanical systems—an assumption in methodological
agreement with the twin principles of simplicity and
the unity of science. In its psychological and philo-
sophical reaches, the idea has come to mean that
psychical events, at least in theory, are empirically
attributable, according to specific, regular, and deter-
minable patterns, to neural mechanisms, without it
being obligatory to define, whether a priori or a
the underlying causation or the ontological
status of mind.


Since around 1900, the man-machine has been a
pervasive idea in the three disciplines—namely, biol-
ogy, psychology, and philosophy—among which its
career and promise continue mainly to be shared. In
each case, however, it has come to have a different
sort of relevance. In the biological sphere, the ever
more exact clarification of the physicochemical
processes of the organism—and of the electrochemical
properties of its nervous component—has had the cu-
mulative effect of justifying the experimental proce-
dures and theoretical standpoint of the “mechanists.”
Nevertheless, the status of the man-machine remains
contingent upon the centuries-old, still unsettled con-
troversy between vitalism and mechanism. An episode
in that debate which might seem pertinent here oc-
curred when E. Rignano published Man Not a Machine,
A Study of the Finalistic Aspects of Life
(1926), and
was promptly refuted by J. Needham's Man A Machine,
in Answer to a Romantical and Unscientific Treatise

(1928). The vitalistic contention that the organism,
while admittedly a physical system, cannot be under-
stood in terms of the same fundamental laws exempli-
fied by the behavior of inorganic mechanisms, remains
tenable as long as living things cannot be synthesized
in the laboratory, despite the methodological sterility
and diminishing plausibility that may be reproached
against it. The thrust of vitalism, at any rate, has been
to deny that man is accurately describable as a ma-
chine, apart from the question whether his psychic
being is or is not a dependency of his body.

Twentieth-century psychology, although it has been
largely unconcerned with deciding if the brain works
“mechanistically” or “organismically,” has in various
other ways embodied or corroborated some form of
the man-machine idea. The highly specialized interest
in animal psychology initiated by John B. Watson and
pursued by the behaviorists has lent weight to the
man-machine by virtue of the uniformity it supposes
between the more mechanical and predictable acts of
animals and those, seemingly less so, of human beings.
Thus, the comparison of man and animal under a single
psychological perspective in our time has been an
experimental reenactment of the speculative step
which, during the seventeenth and eighteenth cen-
turies, had already transformed the beast-automaton
into the man-machine. More broadly, behaviorism has
coincided with the standpoint of human mechanism
in proportion as it has limited itself to observing the
mind nonsubjectively from without, for such happens
to be also the only way in which the behavior of a
machine can be perceived and explained. Conversely,
it is only the external or “public” behavior of a human
being that the machine is able to simulate. To insist
on a psychology restricted to behavior alone makes
psychology, therefore, the science of machines no less
than of animals or men. By excluding from consid-
eration what is least amenable to mechanistic analo-
gies—that is, consciousness and subjective states—
behaviorism has given a blanket endorsement to the
man-machine. In the case of Freudian psychology, it
may be said that the blurring of the ordinary distinction
between voluntary and involuntary actions as a result
of the role of the unconscious, has corroborated the
same idea by suggesting that conscious thoughts and
desires are continuations, on a different plane, of those
instinctual forces—in particular, the sexual—which
manifestly originate in the organism. Psychoanalytic
exploration of countless “unconscious mechanisms” has
brought to light and catalogued a whole new province
of “automatisms” in the life of the psyche. The primacy
of instincts (or “drives”) arising from the biological
makeup of the animal or human being has been the
standpoint, similarly, of the purposive psychology as-
sociated with the names of McDougall and Tolman.
While its various exponents have differed over the
degree of physiological determinism involved, the the-
ory of “drive” has generally been useful to the man-
machine doctrine by providing a sort of nexus for
mechanistic and motivational accounts of psycho-
dynamics. Hull, moreover, has stressed the neurological
basis of motivation to the point of asserting the
isomorphism of cerebral and mental structures, and of
envisaging a science of psychology guided by the
homeostatic principle. This science of man would be
deducible (at least hypothetically) from physiological
postulates about stimuli issuing from the external and
internal environment of the organism, and from in-
herited neural connections between receptors and
effectors. Köhler has realized, in the attempt to explain
visual perception, a synthesis of Gestaltist and
mechanistic hypotheses by the extension of physical
field theory to cerebral functioning. No less significant
for the man-machine position, however, has been the
impressive advance of psychophysiology itself in our
era. The role of endocrinological factors, although
perhaps overestimated a few decades ago, has, none-
theless, been fitted conspicuously into the overall pic-
ture of how the body controls the mind. The impor-
tance of glandular determinants is reflected in the
human typologies that Kretschmer and Sheldon have
worked out by means of statistical correlations between
personality and physique. Continuing research, aided
by new techniques of localization, has greatly perfected
the functional topography of the brain, particularly in
regard to the roles of the mid-brain and brain-stem,
as well as their patterns of integration with one another
and with the cortex. But these technical contributions,
while strengthening the presumption in favor of the


man-machine, also remain problematical. For example,
the investigation of “projection areas” and their inter-
changeability of function has made it more difficult
than before to imagine an exact isomorphism between
mind and brain, or to suggest actual mechanical models
for how the latter performs its task. At the same time,
all of the available psychophysical knowledge can
explain no more than the general features and grosser
aspects of the organic basis of mind. The infinite
diversity that individual thoughts, feelings, and actions
exhibit still remains quite unrelated in any verifiable
sense to specific neural traces or processes.

In contemporary philosophy, the status of the man-
machine is inseparable from the mind-body problem.
Many philosophers would now concede both that the
organism is reducible to the same laws operative in
all nonorganic systems, and that mental events cannot
exist except as the consequences of neural events. But
the real problem lies elsewhere; because if, in the
man-machine formula, biology has been concerned
mainly with the term “machine,” and psychology with
the term “man,” the essential concern of recent philos-
ophy has become the hyphen connecting the two
terms. The decline of dualistic, monistic, and materi-
alistic doctrines founded on the concept of substance
has set the validity of the man-machine thesis in an
entirely different key. Logical positivism has led
Carnap and Neurath to the view that meaningful
statements about the mind are only those which refer
to its outwardly observable properties and can there-
fore be tested. The epistemic form of materialism has
in turn promoted, as best seen perhaps in the work
of Wittgenstein and Ryle, a behavioristic analysis of
mind, the general effect of which has been to construe
“mentalistic” propositions as “physicalistic” proposi-
tions. Such “reductionist” efforts to circumvent the
perennial mind-body dilemma are tantamount to
re-articulating the man-machine idea as a program of
logical reconciliation between two separate universes
of experience and of discourse. More radically consist-
ent with the idea, however, is the “identity theory”
of Feigl, Place, and Smart, which assumes a De facto,
empirical identification of mental states or processes
with states or processes of the central nervous system.
Nevertheless, certain difficulties persist. That every
mental event has its specific causal counterpart in a
neuromechanical event remains a merely hypothetical,
and probably in practice an unverifiable, principle. As
a result, the physicalistic method of analyzing the mind
tends to interpret psychic reality in an idiom which,
when it refers to neural processes, risks becoming
gratuitously indirect and obscure, and, when it refers
to public behavior, fails to express what is given
phenomenologically in consciousness.

The advent of cybernetic technology has greatly
added to the analogical force of the man-machine idea.
The construction of numerous mechanical devices with
purposive and self-adaptive characteristics has had,
first, a decisive impact counter to vitalism, by showing
that modes of behavior long held to be peculiar to
living systems need not necessarily lie beyond the range
of mechanism. Simultaneously, a whole gamut of intel-
lectual capabilities, such as remembering, learning,
judging, foreseeing, problem-solving, etc., have been
simulated by information-fed machines that are able,
among other things, to run mazes, prove theorems,
compose music, play chess, translate from one language
into another, and calculate with an efficiency unap-
proachable by the human mind. The design of these
auto-regulated devices has suggested various useful
hypotheses in neurophysiology and psychophysiology,
especially as regards the mechanism of reflex action
and the neural mechanics of analogous operations
occurring in the brain. Cybernetics has thereby brought
to the man-machine thesis a new dimension borrowed
from electronic technology: notions such as “conduc-
tors,” “circuits,” “signals,” “relays,” “electric charges,”
“thresholds,” “feed-back,” and the like, have gained
currency in attempts to describe the performance of
the central nervous apparatus. The corresponding
model of man that has emerged is a composite of the
earlier physicochemical machine and of a computer-
ized guidance system present within it. While the
influence on philosophy of such technological innova-
tions has been obviously to bolster the postulate that
mental events are somehow identifiable with neuro-
mechanical events, in other respects the contribution
of cybernetics has been controversial and confusing.
It has led, in particular, to the inverse formulation of
the man-machine, that is, to what might be called the
“machine-man” idea—a reversal of things which had,
in fact, always been implicit in the original. Some
philosophers have consequently chosen to deal be-
havioristically with the “mentality” of machines by an
ambivalent or metaphorical use of terms properly
descriptive of human beings and animals. But the
“thinking” in which machines engage is limited nor-
mally to predetermined operations that are, moreover,
reducible to mathematical sequences. It is not easy to
imagine a mechanical analogue of the brain that could
faithfully reproduce the intertexture of all the types
of thinking appropriate to all the situations that human
beings confront, together with the nonlogical modes
through which ideas are associated in the “stream of
consciousness.” Even if such a feat of simulation were
theoretically conceivable, there would be no techno-
logical means of imitating subjective reality. A kind
of dualism thus attaches to mechanistic philosophy


itself as regards the distinction between natural and
artificial machines, the former manifesting a techno-
logic of which consciousness remains the essential and
nonduplicatable trait.

Yet concern about the “mentality” of machines in
contemporary thought is symptomatic of the sociocul-
tural meaning that the man-machine has acquired in
post-industrial societies on the threshold of automation.
The technical superiority of the machine, by trans-
forming mere efficiency into a human ideal, has set
in motion a convergence between itself and man which
tends, on the one hand, to lift the robot to a sort of
sub-human role, and on the other, to assimilate man
to the machine not only in the biological or psycho-
physiological sense, but also in relation to his values
and conduct. Such an invasion of man's private world
by criteria typical of automata has provoked, under-
standably, a reaction which raises the problem of how
far his nature may be equated with that of the machine.
The golem, which in sixteenth-century Yiddish folklore
was envisaged as a beneficent servant of man, has
spawned in our own time a numerous progeny of
“mechanical creatures” about whose intentions we are
far less confident. The obsessive leitmotiv, so popular
in science fiction, of human civilization being threat-
ened by a robot takeover, would seem thus to betray
symbolically a widespread fear of the automatization
of life; for the menacing robot rival is actually man
himself perceived in a depersonalized future shape.

In conclusion, the man-machine idea may be said
at present to occupy a strategic and fateful position
at the confluence of several disciplines and traditions:
in neurophysiology and psychology it is above all a
fecund empirical hypothesis of indefinite promise to
research; in philosophy, it is a speculative option in
the attempt to resolve the body-mind problem; in
technology, it expresses the demiurgic goal of master-
ing our environment by the mechanical maximation
of our limited powers; and as a theme in sociology
and the imaginative arts, it most often conveys the
malaise of dehumanization in modern culture, and
conjures up fantasies that put in doubt the survival of
man's authentic self.


George S. Brett, History of Psychology, ed. R. S. Peters
(London, 1962; New York, 1963). John Cohen, Human
Robots in Myth and Science
(London, 1966; South
Brunswick, N.J., and New York, 1967). K. Gunderson, Men-
tality and Machines
(Garden City, 1971). Heikki Kirkinen,
Les Origines de la conception moderne de l'Homme-Machine
(Helsinki, 1960). F. A. Lange, The History of Materialism
(New York, 1950; original German edition, 1865). Leonora
C. Rosenfeld, From Beast-Machine to Man-Machine: Animal
Soul in French Letters from Descartes to La Mettrie
York, 1941). Aram Vartanian, Diderot and Descartes: A Study
of Scientific Naturalism in the Enlightenment
1953); esp. Ch. IV; idem, La Mettrie's L'Homme Machine:
A Study in the Origins of an Idea,
critical edition with
an introductory monograph and notes (Princeton, 1960).

The translations for Descartes are by the author of the


[See also Behaviorism; Dualism; Epicureanism and Free
Historical and Dialectical Materialism; Necessity;
Organicism; Positivism; Psychological Ideas in Antiquity;
Pythagorean...; Unity of Science.]