III. NEWTON AND LEIBNIZ
“Mechanism” is sometimes defined as the view that
the
phenomena of nature are to be explained by the
motion of bodies having only
geometrical properties.
In this sense of the term, neither Isaac Newton
nor
G. W. Leibniz can be said to have advocated mecha-
nism or subscribed to the mechanical philosophy.
Both
distinguished motion and change of motion from the
forces
required to bring them about; and, though they
thought that these forces
were measurable, they did
not attempt to identify them with the properties
by
which they were measured. Nor, in their accounts of
the nature and
properties of bodies, were they pre-
pared to
reject in its entirety the scholastic doctrine
of fourfold causation,
though both excoriated attempts
to explain particular phenomena by invoking
occult
qualities and forms.
Defining “force” as the “causal principle of
motion
and rest,” Newton attributed to bodies an internal
force—vis insita or vis inertiae—“by which
existing
motion or rest is conserved in a body, and by which
any being
endeavors to continue in its state and op-
poses
resistance” (“De gravitatione et aequipondio
fluidorum,” Unpublished Scientific Papers of
Isaac
Newton, ed. Hall and Hall, p. 148). This force was
listed
as one of the essential properties of bodies and was
distinguished from external forces and active princi-
ples, such as the force of attraction or gravity.
Although
Newton did not include gravity, along with vis
inertiae,
among the essential properties of bodies, he
thought
that it was a universal property; and, when the charge
was
raised that gravity was an occult quality, enjoying
the same dubious status
as the forms and qualities of
the scholastics, Newton insisted that it was
a “mathe-
matical
force,” the existence of which was attested by
experience. He
also denied that, in positing this force,
he had attempted to explain, or
give the cause of,
gravity. On this point, Leibniz, seems to have misun-
derstood him; for, like Leibniz, he
thought that the
notion of bodies acting on one another at a distance
was
unintelligible, and he professed ignorance of the means,
physical
or spiritual, by which gravitation was effected.
Attacking the Cartesian view that the essence of
bodies was simply
extension, Newton adapted scholas-
tic
terminology in presenting his own view. Space or
extension, of which God
was causa emanativa and
which was coeternal
with God, was the materia prima
on which God,
in creating bodies, imposed impene-
trability and form; and “that product of the divine will
is the form or formal reason of body denoting every
dimension of space in
which body is to be produced”
(“De
gravitatione...,” p. 140). Newton hastened to
add, however, that
his notions of materia prima and
substantial
form differed from the nebulous notions of
his predecessors.
Leibniz, also rejecting the Cartesian conception of
matter, contended that
the simple substances or
monads of which bodies were constituted were un-
extended centers of force. By
“force,” he explained,
he meant “something
between the capacity and action,
something which includes an effort, an
act, an en-
telechy... [and] passes of itself
into action, in so far
as nothing hinders it” (Leibniz, Philosophischen Schrif-
ten, ed. C. I. Gerhardt, IV, 472). Motion and geometri-
cal properties, like the sensible
properties—heat, color,
etc.—were appearances or
well-grounded phenomena
(phaenomena bene
fundata). According to Leibniz,
each monad mirrored the universe
from a particular
point of view, and there was harmony or corre-
spondence in the states of the
various monads. But
these correspondences did not result from, nor consti-
tute, efficient causation among monads.
Each state or
property of a monad followed from its given nature;
and,
though it was not incorrect to speak of causation
among monads, this was
“final” or “ideal” causation
based on God's having formed monads in advance in
such a way that they
accommodated themselves to one
another. In his metaphysical system, Leibniz
found a
place for each of the traditional four genera of causes,
distinguishing materia prima and substantial form
and
arguing for the compatibility of explanations by effi-
cient and final causes. He was more charitably
disposed
toward the scholastics than other corpuscular philoso-
phers: they were not, he observed,
entirely to be de-
spised, though they erred in
attempting to explain
particular phenomena by forms and qualities.
The distinction of kinds of causation, along with the
Leibnizian conception
of force, was rejected by Hume
in the Treatise.
Correspondences, in the sense of con-
stant
conjunctions of temporally successive and spa-
tially contiguous objects or events, were ipso
facto
causal relations; and all explanations and inferences
concerning matters of fact were based on relations of
this kind. To many
philosophers of an empiricist or
positivist persuasion, Hume's criticisms
of traditional
views and formulation of a regularity theory of causa-
tion have seemed an impressive and lasting achieve-
ment. Some recent opinion has been more critical.
Concerning the explanation of human behavior, it has
seemed important to
distinguish reasons and causes;
and it has been suggested that, as there
are different
types of causal inquiry, there “may not be a
single
conception of causation but rather a cluster of related
concepts” (H. L. A. Hart and A. M. Honoré,
Causation
in the Law, p. 17).
