Routledge History of Philosophy Volume IV

158 RENAISSANCE AND SEVENTEENTH-CENTURY RATIONALISM
with a picture of the corporeal world in which—because we are only allowed to
ask about the existence of those things of which we have a clear and distinct idea,
and because these are effectively restricted to mathematical concepts—it is little
more than materialized geometry. The deduction of the features of such a world
from first principles is not too hard to envisage.
Nevertheless, there are serious problems with the idea that Descartes is
advocating an a priori, deductivist method of discovery, and I want to draw
attention to four such problems briefly. First, there is the sheer implausibility of
the idea that deduction from first principles could generate substantive and
specific truths about the physical world. The first principles that Descartes starts
from are the cogito and the existence of a good God. These figure in the
Meditations and in the Principles of Philosophy as explicit first principles. Now
by the end of the Principles of Philosophy he has offered accounts of such
phenomena as the distances of the planets from the Sun, the material constitution
of the Sun, the motion of comets, the colours of the rainbow, sunspots, solidity
and fluidity, why the Moon moves faster than the Earth, the nature of
transparency, the rarefaction and condensation of matter, why air and water flow
from east to west, the nature of the Earth’s interior, the nature of quicksilver, the
nature of bitumen and sulphur, why the water in certain wells is brackish, the
nature of glass, magnetism, and static electricity, to name but a few. Could it
seriously be advocated that the cogito and the existence of a good God would be
sufficient to provide an account of these phenomena? Philosophers, like
everyone else, are occasionally subject to delusions, and great claims have been
made for various philosophically conceived scientific methods. But it is worth
remembering in this connection that Descartes is of a generation where method
is not a reflection on the successful work of other scientists but a very practical
affair designed to guide one’s own scientific practice. It is also worth
remembering that Descartes achieved some lasting results in his scientific work.
In the light of this, there is surely something wrong in ascribing an unworkable
methodology to him.
Second, Descartes’s own contemporaries did not view his work as being
apriorist and deductivist, but rather as being committed to a hypothetical mode
of reasoning, and, in the wake of Newton’s famous rejection of the use of
hypotheses in science, Descartes was criticized for offering mere hypotheses
where Newtonian physics offered certainty. 5 A picture of Descartes prevailed in
his own era exactly contrary to that which has prevailed in ours, and, it might be
noted, on the basis of the same texts, that is, above all the Discourse on Method,
the Meditations and The Principles of Philosophy. The possibility must therefore
be raised that we have misread these texts.
Third, if one looks at Descartes’s very sizeable correspondence, the vast bulk
(about 90 per cent) of which is on scientific matters, one is left in no doubt as to
the amount of empirical and experimental work in which he engaged. For
example, in 1626 Descartes began seeking the shape of the ‘anaclastic’, that is,
that shape of a refracting surface which would collect parallel rays into one