C CUNYB/Clarke December, :
AFabulous World (–) The extremely simple, and therefore readily intelligible, features of matter
in motion were considered by its author to have a decisive advantage in
comparison to the multiplicity and complexity of the forms to which
scholastic philosophers appealed. By adding three laws of nature to this
simple story, Descartes thought he had provided enough to construct a
physical theory of the universe.
The first of Descartes’ laws of nature is that ‘each individual part of
matter always continues to be in the same state, as long as it is not forced
to change that state by collision with others’ (xi.). He argued that
almost everyone accepts that law when it is applied, for example, to the
shape of a piece of matter or to the fact that it is stationary. Things do
not change shape spontaneously or begin to move from a position of rest
without some cause. All he did, therefore, was to extend the same rule
to the motion of bodies. If something is in motion, then no new cause is
required to explain why it remains in motion; but if its motion is changed –
in speed or direction – then we must look for the factor that caused the
change. The second law describes, in quantitative terms, how motion is
transferred from one body to another on impact, and it is proposed as an
hypothesis. ‘When one body pushes another, it could not contribute any
motion to the other except by simultaneously losing as much of its own
motion, nor could it take away any of the other’s motion unless its own
motion increases by the same amount’ (xi.). The third and final law of
nature is the law of rectilinear motion: ‘when a body moves[,]...each of
its parts individually always tends to continue its motion in a straight line’
(xi.–).
These three laws of nature are qualified in two ways. They are not the
only relevant laws, and they are inserted into a metaphysical or theological
background that does little to confirm their truth but goes some distance
toward separating nature from the Creator, who is normally regarded as
the ultimate cause of all phenomena. On the adequacy or otherwise of
the three laws, Descartes writes that ‘I shall provide here two or three of
the principal rules according to which one must think that God causes the
nature of this new world to act and which will be enough, I believe, to let you
know all the others’ (xi.). Once the three rules have been proposed,The
Worldacknowledges the need for ‘many rules’ to ‘determine in detail when,
and how, and by how much, the motion of each body may be diverted, and
increased or decreased, by colliding with other bodies’ (xi.). However,
readers are left to work out these applications themselves.