UNITY OF PRINCIPLES 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
posteriora 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,
Prooemium).
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-
tiarum, 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-
physics, 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-
particulars.)
