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Dictionary of the History of Ideas

Studies of Selected Pivotal Ideas

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The professors of wisdom in Greece did pretend,”
says Francis Bacon, “to teach a universal Sapience....
And it is a matter of common discourse of the chain
of the sciences how they are linked together, insomuch
that the Grecians, who had terms at will, have fitted
it of a name of Circle Learning” (Valerius Terminus,
Ch. I, Works, VI, 43). The ideal of such a universal
knowledge has played a dominant role in the course
of European culture, both scientific and humanistic,
whether expressed in the educational requirements for
merely the Roman orator and architect or at its apogee
in the eighteenth-century Encyclopédie for the
enlightenment of a whole age. It is partly in relation
to this ideal that the more limited concept of the unity
of the exact sciences arises; partly, however, it arises
from the nature of science itself. In a science the search
for unity and for intelligibility are inseparable. It is
natural for this search to extend itself beyond the
confines of the individual science to all the sciences
taken together.

The main conception of the unity of the sciences
until the time of Kant can, for convenience of classifi-
cation, be considered in relation to the ways in which
the sciences were in general, following Aristotle, dis-
tinguished from one another: (1) by their principles
or logical foundations, (2) by their subject matters, and
(3) by their methods. Consequently there are concep-
tions of unity underlying the principles of the different
sciences, of unity with respect to their subject matters,
and of unity with respect to their methods. To these
we can add a fourth conception of unity with respect
to the end or ends of science.


In the case of principles two powerful traditions
were established by Plato and Aristotle. Plato distin
guished the five mathematical arts (arithmetic, plane
and solid geometry, astronomy, and harmonics), from
all the other arts, for though, like the others, they are
undertaken for their practical utility, they contain
some apprehension of true being. Those who study
them, however, accept their principles uncritically as
self-evident or absolute and no attempt is made to
account for them. Plato envisaged a science, “dialec-
tic,” which is superior to the mathematical sciences,
because it takes their assumptions not as principles,
but as hypotheses, using them as stepping stones for
ascending to a single principle, not itself hypothetical,
the first principle of everything, or the Form of the
good. In doing so dialectic destroys their hypothetical
character, that is, renders them intelligible or known,
for “that which imparts truth to the things that are
known and the power of knowing to the knower you
affirm to be the Form of the good. It is the cause of
knowledge and truth” (Republic 508). Moreover,
dialectic shows the interconnections of the sciences
with one another and their relation to the nature of
being. Plato asserts it to be the distinguishing mark
of the dialectician that he has the ability to see the
sciences as comprising one whole (ibid. 537).

In opposition to the Platonic conception of the unity
of the sciences with respect to their principles, there
is the Aristotelian view which denies the possibility
of a supreme science from which the basic truths of
the particular sciences can be deduced (Analytica
76a 16-25). These basic truths are indemon-
strable. Nevertheless there is a science which embraces
the others. “We suppose,” says Aristotle, “that the wise
man knows of all things, as far as possible, although
he has not knowledge of them in detail” (Metaphysica
982a 10). “In knowing the most universal things he
knows in a sense all the instances which fall under the
universal” (ibid. 23). While each of the special sciences
investigates some kind of being with a view to demon-
strating its essential properties, the highest degree of
universal knowledge, or first philosophy, investigates
the properties of no genus, but only the properties of
being as being. Included also in first philosophy are
the common principles or axioms which hold for
everything that is insofar as it is and not insofar as
it belongs to some genus. The most certain of these
is the principle that “the same attribute cannot at the
same time belong and not belong to the same subject
and in the same respect” (ibid., 1005b 19). Aristotle
also mentions the law of excluded middle. Among the
indemonstrable basic truths of a science some are pe-
culiar to that science and some are common to all the
sciences, “but common only in the sense of analogous,
being of use only in so far as they fall within the genus
constituting the province of the science in question”


(Analytica posteriora 76a 37). Taking “common” in this
sense, Aristotle says, “In virtue of the common ele-
ments of demonstration—I mean the common axioms
which are used as the premisses of demonstration, not
the subjects or the attributes demonstrated as belonging
to them—all the sciences have communion with one
another” (ibid. 77a 26).

With the rediscovery of Aristotle in the West in the
thirteenth century, the conception of a universal sci-
ence of being as being emerges again. In his Commen-
tary on Aristotle's Metaphysics Saint Thomas Aquinas
defines metaphysics as the science which investigates
the most intelligible things, that is to say, the most
universal principles. These are being and the conse-
quent attributes of being, such as one and many,
potency and act. Without knowledge of these universal
principles it is not possible to have a complete knowl-
edge of any genus or species of things. Moreover, it
should not be left to any one of the particular sciences
to investigate these principles, for, as necessary to the
knowledge of any genus whatever, they would equally
have to be investigated in all the particular sciences.
Aquinas concludes that there must be one universal
science whose concern is these principles (Expositio,

It is not possible here to trace the meanings attached
to “being” from Aristotle through the periods of scho-
lasticism and into the eighteenth century when it be-
came, as the highest abstraction, the vacuous subject
of Wolff's ontology, a science given pride of place in
the classification of the sciences in the Discours prélim-
inaire de l'Encyclopédie.
However, in the seventeenth
century Francis Bacon, for the specific purpose of
giving unity to the sciences, took over the Aristotelian
notion of first philosophy, and adapted it to his own
thoroughgoing philosophical materialism, substituting
nature for being. For Bacon first philosophy is a uni-
versal science, “the mother of the rest,” and prior to
all divisions by subject matter (De augmentis scien-
Book III, Ch. I, Works, VIII, 471). It has two
parts. First, it is a repository of all axioms not peculiar
to any of the particular sciences. Unlike the axioms
of Aristotle's first philosophy, however, they are not
common to all the sciences, but are such as are shared
by two or more. Moreover, where for Aristotle it is
impossible in demonstration to pass from one genus
to another, the principle function of the axioms for
Bacon is precisely that of making these transitions
possible, “in order that solution of continuity in sci-
ences may always be avoided. For the contrary thereof
has made particular sciences to become barren,
shallow, and erroneous” (ibid., Book IV, Ch. I, Works,
IX, 14). Secondly, first philosophy is a doctrine of
transcendentals (Being, One, etc.), but again with im
portant modifications of tradition. Where for the scho-
lastics being was the first of the transcendentals, and
the others were coextensive or convertible with it,
either singly, as in the case of unity, truth and goodness,
or in disjunction as in the case of substance-accident,
necessary-contingent, actual-potential, etc., Bacon
presents a list only of disjunctive transcendentals and
assigns being to membership in one of the disjunctive
pairs—“Much, Little; Like, Unlike; Possible, Impossi-
ble; likewise Being and Not Being, and the like” (ibid.,
Book III, Ch. I, Works, VIII, 473). He does not appear
to regard these pairs of disjunctives as coextensive with
anything. What he considers important, however, is
that first philosophy be concerned with “the operation
of these Common Adjuncts” insofar as “they have
efficacy in nature,” and without regard to divisions of
the sciences.

Plato's notion that there is a single science which
gives certainty to the principles of the other sciences
emerges again in the seventeenth and eighteenth
centuries, most notably with Descartes, Leibniz, Hume,
and Kant. Descartes' metaphysics gives certainty to the
other sciences in two ways; one, by the removal of
the hyperbolical doubt to which even mathematics is
subject—the atheist mathematician cannot know that
his science is true—and the other by showing that the
Cartesian physics is not merely a new hypothesis but
is true, and that the physics of Aristotle is false. Prior
to producing his Principles of Philosophy Descartes
presented all his treatises in the physical sciences as
resting on hypothetical principles, which, though
confirmable by experience, he considered himself able
to deduce from the primary truths of his metaphysics
(Discourse on Method, Part VI). Later he was to claim
for his Meditations that they “contain the entire foun-
dations of my physics” or “contain all its principles”
(Oeuvres, III, 297f., 233). It is more specifically Medi-
tation V,
determining the essence of material things
to be extension, and Meditation VI, establishing the
real distinction between the mind and the body, which
banish substantial forms from nature and demonstrate
that all physical phenomena, including living phenom-
ena, whether plant, animal, or human, are governed
by purely mechanical principles. These principles are
extended even to the scientific treatment of the pas-
sions: “my aim has been to explain the passions...
only as a physicist” (ibid., XI, 326). Thus Descartes
aptly compared philosophy as a whole to “a tree,
whose roots are metaphysics, whose trunk is physics,
and whose branches, which issue from this trunk, are
all the other sciences,” in particular, medicine, me-
chanics, and morals (Principia philosophiae, Preface).

Leibniz attributes a similar role to metaphysics in
relation to the natural sciences, but for different rea-


sons. Because physical nature is the phenomenal
expression to a perceiver of immaterial or metaphysical
substances, the principles governing phenomena are
ultimately grounded in metaphysical principles. “We
acknowledge that all phenomena are indeed to be
explained by mechanical efficient causes but that these
mechanical laws are themselves to be derived in gen-
eral from higher reasons and that we thus use a higher
efficient cause only to establish the general and remote
principles” (Specimen Dynamicum, Loemker, p. 722).
Physicists must not, like the scholastics with their sub-
stantial forms, introduce metaphysics into physics. The
two spheres are separate. The sole function of meta-
physics in relation to the physical science is to provide
the foundations of their principles (Discourse on Meta-
Sec. X).

What Descartes and Leibniz in their different ways
claimed for metaphysics, Hume claimed for his new
“science of man,” an empirical psychology conceived
by analogy with Newton's natural philosophy. Because
all sciences “return back by one passage or another
to the science of human nature,” Hume proposed “...
to march up directly to the capital or centre of these
sciences, to human nature itself.... From this station
we may extend our conquest over all these sciences.
There is no question of importance, whose decision is
not comprised in the science: and there is none which
can be decided with any certainty, before we become
acquainted with that science. In pretending therefore
to explain the principles of human nature we in effect
propose a compleat system of the sciences, built on
foundations almost entirely new, and the only one on
which they can stand with any security” (Treatise of
Human Nature,
Introduction). Hume mentions seven
sciences: mathematics, natural philosophy, natural re-
ligion, logic, morals, criticism, and politics. Of the first
three he says only that it is, “impossible to tell what
changes and improvements we might make in these
sciences” by bringing the science of man to bear on
them. In the case of the last four sciences Hume carried
out his project thoroughly and psychologized them all.

Kant, too, was to introduce a new science to lay
the foundations of the other sciences. He raised three
questions. How is pure mathematics possible? How is
the pure science of nature possible? How is meta-
physics as science possible? These can all be summed
up in one question, how are a priori synthetic judg-
ments possible, or what are the grounds for taking such
judgments as true? This is the object of a “transcen-
dental” inquiry. The first two of these sciences Kant
considered secure and certain. They actually exist as
sciences and therefore are possible. The only reason
for undertaking an inquiry into their grounds was for
the sake of metaphysics, whose possibility had not yet
been established. Metaphysics for Kant is the same as
for Aristotle, that is, it “considers everything in so far
as it is” (Critique of Pure Reason, B 873). The outcome
of the transcendental investigation was that of showing,
however, that metaphysics is restricted to everything
insofar as it is in nature, that is, insofar as it is an object
of possible experience. Thus the only metaphysics
which is possible is that which he had called the pure
science of nature. Nature includes the objects of both
psychology and physics. Physics becomes a subalter-
nate of this pure science of nature when concepts of
empirical origin such as motion, impenetrability, and
inertia are introduced. Nevertheless physics must use
principles of absolute universality for the whole realm
of nature, both psychological and physical, such as
“every substance is permanent” and “every event is
determined by a cause according to constant laws.”
When Kant speaks of “the pure science of nature,”
he treats it as an existing science in no need of a
transcendental deduction for its own sake. When,
however, he speaks of the same thing under the name
“metaphysics of nature,” then he considers that his
transcendental investigation will put that metaphysics
on “the secure path of a science. For this new point
of view will enable us... to furnish satisfactory proof
of the laws which form the a priori basis of nature”
(ibid., B xix). Moreover it will make possible an
exhaustive knowledge of the principles which consti-
tute this pure science. Kant also provided the same
kind of foundation for the metaphysics of morals as
for the metaphysics of nature, for the supreme princi-
ple of morality is an a priori synthetic practical propo-
sition, and its possibility like that of the a priori syn-
thetic propositions of the other sciences requires a
demonstration in order “to prove that morality is no
mere phantom of the brain.”

(An a priori proposition, in contrast to a posteriori
particular facts, is universal and necessary, e.g., truths
of mathematics, laws of nature, rules of logic; a syn-
thetic proposition, in contrast to an analytic truth by
definition, goes beyond the definition of the subject,
e.g., the planets all move in elliptical orbits around the
sun; an a priori synthetic proposition is a universal,
necessary judgment going beyond definition and sense-


“Let no man,” says Bacon, “look for much progress
in the sciences... unless natural philosophy be carried
on and applied to particular sciences and particular
sciences be carried back again to natural philosophy.”
This holds not only for “astronomy, optics, music, a
number of mechanical arts, medicine itself,” but also
for “what one might more wonder at, moral and polit-


ical philosophy, and the logical sciences” (Novum
Book II, Aph. lxxx, Works, VIII, 112). Bacon
does not regard these other sciences as parts of natural
philosophy, but as having their “roots” in it. Natural
philosophy itself, however, contains within it certain
constituent sciences which form a pyramid. These are
distinguished from one another not by their subjects,
but by their levels of generality in knowledge of the
one subject, nature. At the base of the pyramid is
natural history. On that is built physics, which has two
parts, one less general and one more general. On
physics is built metaphysics (a science distinct from
first philosophy) which brings the axioms of physics
under still more general axioms. At the vertical point
of the pyramid is “the summary law of nature”—i.e.,
“the force implanted by God in the first particles of
matter from the multiplication whereof all the variety
of things proceeds and is made up” (De principiis,
X, 345), though knowledge of it is probably
beyond the reach of the human mind. The three
inductively ordered levels, natural history, physics, and
metaphysics, are “the true stages of knowledge.” Given
the one subject, nature, it is Bacon's logic of induction
which alone determines both the divisions and the
unity of the sciences which comprise natural philoso-
phy. Bacon also divided all human learning on the basis
of Memory (History), Imagination (Poetry), and Reason

Hobbes's materialism taken in conjunction with his
logic or method has similar reductive consequences for
the division and unity of the sciences, though the
method is now deductive, not inductive. As knowledge
of causes, science is in every case knowledge of the
motions of bodies by which effects are generated. These
motions are the single subject of all sciences, one sci-
ence being distinguished from another only by the
complexity of the motions which it investigates. Thus
after first philosophy—which consists of definitions of
the most general names—comes geometry, the science
of the simple motions of a body by which lines, sur-
faces, and figures are produced. Then follows the sci-
ence concerned with the effects of the impact of
moving bodies; then the science of the effects of the
internal motions of bodies, that is, physics or the study
of sensible phenomena such as light, colors, sounds,
tastes, odors, heat, etc., and of the senses themselves;
then moral philosophy or the science of the motions
of the mind such as appetite, aversion, love,
benevolence, etc., for these are motions consequent
upon the motions of sense; and finally, because the
motions of the mind are the causes of the common-
wealth, there comes civil or political philosophy (Con-
cerning Body,
Ch. VI, Secs. 6, 7).

For Spinoza and Leibniz also the sciences are not
diversified by the kinds of beings which they investi-
gate. There is for Spinoza only one substance, God or
nature, and for Leibniz only one kind of substance,
monads. In Spinoza's world the essence of any individ-
ual finite thing is the power or effort by which it
endeavors to persevere in its being. This conatus fol-
lows from, or is a mode of, the infinite power of God,
a power which can be expressed to the perceiving
intellect either as infinite extension or as infinite
thought (Ethics, Part I, definitions 4, 6). Corre-
spondingly, the conatus constituting the essence of the
individual thing can be expressed either as body or as
mind. Thus physics on the one hand and the science
of the thoughts and emotions of the mind on the other
are knowledge merely of the same conatus, but as
differently expressed, and the order of causes in the
one science will be identical with the order of causes
in the other (ibid., Part II, prop. 7). Spinoza's proposed
aim of acquiring “the knowledge of the union which
the mind has with the whole of nature” required the
study of Moral Philosophy, the Theory of the Educa-
tion of Children, the science of Medicine and the art
of Mechanics (De emendatione, II, 13-15). Leibniz too
adopts a double aspect conception, but in his case it
is used for correlating metaphysics, the science of
beings as they are in themselves, that is, as indivisible
spiritual substances, with physics, the science of these
same beings as they appear, that is, as material
phenomena or extended masses. “These two realms are
distinct, each one being governed by its own laws....
But the two very different series are in mutual corre-
spondence in the same corporeal substance and
harmonize so perfectly that it is just as if one were
ruled by the influence of the other” (Loemker, p. 675).


According to Aristotle there is not a single method
applicable to all subject matters, but each has its own
appropriate method (Metaphysica 995b; De anima
402a; Ethica 1094b). While this was being reiterated
by Saint Thomas in the thirteenth century, two of his
contemporaries formulated conceptions of a universal
method of discovery applicable in all the sciences;
Roger Bacon in his scientia experimentalis, and
Raymond Lully in his ars magna, the one empirical,
the other a priori. Bacon calls his experimental science,
“this great mistress of the speculative sciences,”
attributing to it “the same relation to the other sciences
as the science of navigation to the carpenter's art and
the military art to that of the engineer.... It directs
other sciences as its handmaids, and therefore the
whole power of speculative science is attributed espe-
cially to this science” (Opus maius, Part VI, p. 633).
Knowledge is acquired in two ways, either by reasoning


or by experience. Experience includes what is learned
not only through the external senses but also through
internal illumination or divine inspiration, the latter
being important for both religion and for the principles
of the speculative sciences. Bacon worked out no rules
of operation for his new experimental science and it
is not a precursor of his namesake's logic of induction.
However, he assigned to it three prerogatives. The first
is that of verifying conclusions deduced from princi-
ples. This is not so much a method of testing hypotheses
as of giving certainty to conclusions and removing
doubt, and is not therefore properly a method of
discovery. But in its second and third prerogatives it
is one of discovery. In the second it discovers new
truths within a science which are incapable of being
deduced from the principles of that science, and in
the third it operates without reference to the limits
of any of the particular sciences, but by its own power
investigates the secrets of nature.

Like Bacon, and those in the tradition of Aristotle,
Lully believed that each branch of inquiry rested on
a limited number of principles and basic concepts. To
this he added the notion that if letters of the alphabet
were substituted for these elements, and combined in
every possible way in a purely mechanical fashion,
everything which it is possible to know in that subject
could be discovered. Thus the great art was capable
of yielding universality of knowledge. Lully enjoyed
as great a following among his contemporaries as
Thomas Aquinas and the basic idea underlying the
great art continued to exercise a fascination until the
seventeenth century, when it became incorporated in
the ars combinatoria of Leibniz. But where Lully
assumed that each branch of knowledge had its own
simple elements, Leibniz believed it to be possible to
find a single set of irreducible concepts common to
all the sciences. Once all these concepts were given
their characteristic numbers or signs, their combina-
tions could generate a complete “demonstrative

Now since all human knowledge can be expressed by letters
of the Alphabet, and since we may say that whoever under-
stands the use of the alphabet knows everything, it follows
that we can calculate the number of truths which men are
able to express, and that we can determine the size of a
work which would contain all possible human knowledge,
in which there would be everything which could ever be
known, written, or discovered; and even more than that,
for it would contain not only the true but also the false
propositions which we can assert, and even expressions
which signify nothing

(ed. Wiener, p. 75).

Leibniz claimed to have derived the basic idea of the
art of combinations from the study of Aristotle's formal
logic, but it was, he says, arithmetic and algebra which
revealed to him the role of signs or characters in
making demonstration in the sciences possible. “It is
as if God, when he bestowed these two sciences on
mankind, wanted us to realize that our understanding
conceals a far deeper secret, foreshadowed by these
two sciences” (trans. Loemker, p. 340).

Descartes too had drawn his inspiration for a uni-
versal method for the sciences from the study of math-
ematics, but what he saw as significant was not, as with
Leibniz, the use of symbols in algebra, but the logical
interconnections of all the parts of geometry. These
“had caused me to imagine that all those things which
fall under the cognizance of man might very likely
be mutually related in the same fashion” (Discourse
on Method,
Part II). This conviction is expressed in
an early opuscule: “All the sciences are interconnected
as by a chain; no one of them can be completely
grasped without the others following of themselves and
so without taking in the whole of the encyclopaedia
at one and the same time” (Oeuvres, X, 255). Descartes
began his first work on method, the Regulae, with an
explicit attack on the Aristotelian specialization of
methods according to subject matter. He did so on two
grounds, first, that the mind in its cognitive exercise
is no more differentiated by its subjects than is the sun
by what it illuminates, and, second, that everything
knowable is logically linked. The logical order, or
“order of reasons” which proceeds from the simpler
to the more difficult, runs directly counter to the “order
of subject-matters,” the latter being “good only for
those for whom all reasons are detached” (ibid., III,
266f.). To isolate a branch of knowledge by subject is
to deprive it of its scientific character and render it
a mere collection. There can therefore be no plurality
of sciences but only one universal science, whose parts
are undifferentiated by subjects. Leibniz took the same
view of his demonstrative encyclopaedia, pointing out
that as in geometry the demonstrative order does not
permit everything belonging to the same subject to be
dealt with in the same place. Because the encyclo-
paedia would result in the dissolution of the divisions
of the sciences by subject, an index would be an essen-
tial part of the project in order to make it possible
to bring together all propositions bearing on any one
subject (New Essays, Book IV, Ch. XXI).

In the eighteenth century the most insistent voice
on the identity of method in all the sciences was
Condillac's. Like Leibniz, he saw the perfect existing
example of this method in algebra, with its use of signs.
Algebra provided “a striking proof that the progress
of the sciences depends uniquely on the progress of
language, and that well constructed languages alone
can give analysis the degree of simplicity and pre-


cision of which it is susceptible” (Oeuvres, II, 409 b).
He did not, like Leibniz, conceive the possibility of
a single language for all the sciences; each would have
its own, while using exactly the same method of analy-
sis. The more radical part of Leibniz' ideal, that of
a universal language, emerges again, however, with
Condorcet. This language would, he says, be like alge-
bra, “the only really exact and analytical language yet
in existence,” containing within it “the principles of
a universal instrument applicable to all combinations
of ideas,” and as easily available to all as the language
of algebra itself (Sketch, pp. 197f.).


Says Socrates in the Republic:

If we do not know the Form of the good, though we should
have the fullest knowledge possible of all else, you know
that that would be of no use to us, anymore than is the
possession of anything without the good. Or do you think
there is any advantage in universal possession if it is not
good, or in understanding the whole world except the good?

(Republic 505).

In its relation to all other knowledge Aristotle's first
philosophy exercises the same function as Plato's
dialectic. It is “the most authoritative of the sciences
and more authoritative than any ancillary science,” for
it knows the supreme good in the whole of nature,
and therefore the end to which the other sciences are
directed (Metaphysica 982b 5). Saint Thomas and the
medieval philosophers follow Aristotle in assigning to
metaphysics the status of ruler of all the other sciences
as directed to one end, and for Kant this legislation
as a regulative guide constitutes the very essence of
philosophy. The pursuit of sciences with a view to
attaining their greatest logical perfection he calls “the
scholastic concept” of philosophy.

But there is likewise another concept of philosophy, a
conceptus cosmicus, which has always formed the real basis
of the term 'philosophy,' especially when it has been as
it were personified and its archtype represented in the ideal
philosopher. On this view philosophy is the science of the
relation of all knowledge to the essential ends of human
reason (teleologia rationis humanae), and the philosopher
is not an artificer in the field of reason, but himself the
lawgiver of human reason

(Critique of Pure Reason, B 867).

Reason, in exercising its purely logical function, is
concerned with bringing the manifold knowledge pro-
vided by the understanding to the highest degree of
systematic unity. It is this unity which distinguishes
science from a mere aggregate of things known. In
pursuit of this end reason is compelled to operate with
the idea of the form of the whole of the science in
question, an idea which determines a priori the scope
of the content of the science and the relation of its
parts to one another. This regulating idea gives the
science the same kind of unity as that possessed by
an animal organism, and just as the parts of each sci-
ence form an organic whole, so also do all the sciences
taken together. “Not only is each system articulated
in accordance with an idea, but they are one and all
organically united in a system of human knowledge,
as members of one whole, and so as admitting an
architectonic of all human knowledge” (ibid., B 863).
This whole of human knowledge will be directed by
an idea, in the same way as is each of its constituent
sciences, in order that the essential ends of reason
served by each will be viewed under one ultimate end,
namely, “the whole vocation of man.” The highest
degree of formal unity in the natural sciences—
psychology, physics, and a third science which is a
systematic union of the first two—is pursued under the
regulative idea of the whole of nature as the work of
a supreme intelligence. Practical reason, or morality
also operates under a regulating idea, that of a King-
dom of Ends. This idea provides a means of formulating
the moral law: “every rational being must so act as
if he were by his maxims in every case a legislating
member in a universal kingdom of ends.” Such a king-
dom could be realized only if nature harmonized with
human ends, that is, only if the kingdom of nature and
the kingdom of ends were united under one supreme
ruler. Hence the moral idea of God is that supreme
regulating idea which brings all the sciences into sys-
tematic unity in the science of moral theology. It is
moral theology which “enables us to fulfill our voca-
tion,” or attain our highest end.


The Works of Aristotle Translated into English, ed. J. A.
Smith and W. D. Ross (Oxford, 1908-52). The Works of
Francis Bacon,
ed. Ellis, Spedding, and Heath (Boston, 1864).
The Opus Maius of Roger Bacon, trans. R. B. Burke (Phila-
delphia, 1928). Oeuvres philosophiques de Condillac, ed.
Georges Le Roy (Paris, 1947-51). A. N. de Condorcet, Sketch
for a Historical Picture of the Progress of the Human Mind

(1795), trans. J. Barraclough (New York, 1955). Oeuvres de
ed. C. Adam and P. Tannery (Paris, 1897-1913).
The English Works of Thomas Hobbes, ed. W. Molesworth
(London 1839-45). D. Hume, A Treatise of Human Nature
(1739-40), ed. L. A. Selby-Bigge (Oxford, 1888). I. Kant,
Critique of Pure Reason, trans. N. K. Smith (London, 1933).
G. W. Leibniz, Selections, ed. P. P. Wiener (New York, 1951).
New Essays Concerning Human Understanding (1704) trans.
A. G. Langley (LaSalle, Ill., 1949). Gottfried Wilhelm Leib-
niz, Philosophical Papers and Letters,
trans. and ed. L. E.
Loemker (Chicago, 1956). Raymundi Lullii Opera ea quae
ad adinventam ab ipso artem universalem... pertinent

(Strassburg, 1617). Plato, Republic, trans. A. D. Lindsay


(London, 1920). The Chief Works of Benedict de Spinoza,
trans. R. H. M. Elwes (London, 1883-84). Thomas Aquinas,
Expositio in libros Metaphysicorum, ed. M. R. Cathala and
R. M. Spiazzi (Turin, 1950); The Division and Methods of
the Sciences, Questions V and VI of his Commentary on
the De Trinitate of Boethius,
trans. with an introduction by
Armand Maurer (Toronto, 1953).


[See also Baconianism; Causation, Final Causes; Certainty;
Classification of the Sciences; Enlightenment; God; Platon-