less interesting than the earlier destructive part. It uses all sorts of scholastic maxims, such as that
an effect can never have more perfection than its cause, which have somehow escaped the initial
critical scrutiny. No reason is given for accepting these maxims, although they are certainly less
self-evident than one's own existence, which is proved with a flourish of trumpets. Plato's
Theaetetus, Saint Augustine, and Saint Thomas contain most of what is affirmative in the
Meditations.
The method of critical doubt, though Descartes himself applied it only half-heartedly, was of great
philosophic importance. It is clear, as a matter of logic, that it can only yield positive results if
scepticism is to stop somewhere. If there is to be both logical and empirical knowledge, there
must be two kinds of stopping points: indubitable facts, and indubitable principles of inference.
Descartes's indubitable facts are his own thoughts--using "thought" in the widest possible sense. "I
think" is his ultimate premiss. Here the word "I" is really illegitimate; he ought to state his
ultimate premiss in the form "there are thoughts." The word "I" is grammatically convenient, but
does not describe a datum. When he goes on to say "I am a thing which thinks," he is already
using uncritically the apparatus of categories handed down by scholasticism. He nowhere proves
that thoughts need a thinker, nor is there reason to believe this except in a grammatical sense. The
decision, however, to regard thoughts rather than external objects as the prime empirical
certainties was very important, and had a profound effect on all subsequent philosophy.
In two other respects the philosophy of Descartes was important. First: it brought to completion,
or very nearly to completion, the dualism of mind and matter which began with Plato and was
developed, largely for religious reasons, by Christian philosophy. Ignoring the curious transactions
in the pineal gland, which were dropped by the followers of Descartes, the Cartesian system
presents two parallel but independent worlds, that of mind and that of matter, each of which can
be studied without reference to the other. That the mind does not move the body was a new idea,
due explicitly to Geulincx but implicitly to Descartes. It had the advantage of making it possible
to say that the body does not move the mind. There is a considerable discussion in the Meditations
as to why the mind feels "sorrow" when the body is thirsty. The correct Cartesian answer was that
the body and the mind were like two clocks, and that when one indicated "thirst" the other