4. Matter in Metaphysical Thought: Locke and
Leibniz. By the time of Newton the progressive spe-
cialization that has distinguished physicists, chemists,
and other empirical students of matter from the phi-
losophers and metaphysicians was fairly well advanced.
The history of the concepts of matter becomes corre-
spondingly complex. On the one hand as the scientists
have achieved greater determinacy regarding particu-
lar properties of kinds of matter, they have on the
whole been more content to leave indeterminate the
question of its ultimate generic nature: by the end of
the eighteenth century Lavoisier was insisting on that
exclusive concentration of his interests. On the other
hand, while philosophers have not ceased their effort
to excogitate what matter must be and cosmologies
have still been produced, more interestingly perhaps,
because cosmology has not been the center of philo-
sophical interest, theories of matter have been derived
from, or even only implied by, disciplines that were—
epistemology, semantics, theories of action. Neither
Karl Marx's revolutionary program of action nor A. J.
Ayer's positivist theory of meaning were indefinitely
flexible as to how matter, or “the physical world,”
were conceived. Both would find some features of some
theories of matter we have considered incompatible
with their views, and that is to say that their pragmatic
and semantic theories have implications for a theory
of matter. We may illustrate by the roles matter plays
in two contemporaries of Newton, John Locke and
G. W. Leibniz when the principal preoccupations of
philosophy tended, after the revolution of Descartes,
to be epistemological.
Locke and Leibniz are often cited as paradigm in-
stances of (British) “empiricism” and (Continental)
“rationalism,” but these commitments, and their own
curiosity, pushed them to fairly explicit concepts of
matter, even though it was the primary concern of
neither. Consider contrasting definitions of “sub-
stance.” Locke says that “... substance is supposed
always [to be] something besides the extension, figure,
solidity, motion, thinking [in the mental substances
which he also recognizes], or other observable ideas,
though we know not what it is” (Essay Concerning
Human Understanding II. 23. 3). Since, we know only
that there must be something capable of causing these
ideas of itself in us, “Powers therefore justly make a
great part of our complex ideas of substances” (ibid.,
10; cf. Mill's “permanent possibility of sensation”;
Mach's phenomenalism). In terms of the criteria that
have here been employed to distinguish concepts of
matter, Locke's procedure might be described as the
“materialization” of all substance, for he made it stuff,
underlying and persisting through our experience,
concrete and ostensible but itself defying any repre-
sentative formulation.
But for Leibniz “... this is the nature of an individ-
ual substance or of a complete being, namely, to afford
a conception so complete that the concept shall be
sufficient for the understanding of it and for the deduc-
tion of all the predicates of which the substance is or
may become the subject...” (Discourse on Meta-
physics VIII). Of course Leibniz was speaking of his
monads, psychic substances, each of which mirrored
the entire universe from a unique angle of observation.
Even that expression is misleading for the orders of
space, time, and phenomenal matter were derivative
from the internal structure of individual concepts
rather than vice versa. Leibniz has identified substance
wholly with what is formal, defining, structural, and
intelligible. Material substance has become, for
Leibniz, only a phenomenon bene fundatum, a con-
ceptually useful matrix for ordering phenomena.
There are many ways, by no means all of them
touched on here, in which Locke is “Democritean”
and Leibniz is “Platonic” though a just account would
have to include very significant differences as well. The
“Aristotelian” alternative of finding in objects of in-
quiry both actual and knowable aspects (“form”) and
also as their ground, still mysterious potentialities and
powers (“matter”), was certainly also present in the
seventeenth century—to some extent in Newton's con-
fidence that he had discovered real forces operative
in the world combined with his uncertainty as to what
their precise nature was.
There seems little doubt that awareness of different
historical concepts of matter can be a factor in further
inquiry into matter itself. The history of the astonishing
progress that has been made in that direction finds the
same or similar conceptual schemes now opening the
way for, now obstructing, particular insights and dis-
coveries. But so long as we continue to be confronted—
through highly sophisticated devices of detection, or
through ordinary gross observation—by something sen-
sibly and convincingly there, additional to and un-
exhausted by our ideas and formulae, something like
the concept of matter will have work to do.
