Descartes: A Biography

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The French Liar’s Monkey and the Utrecht Crisis 

than various dispositions of matter in motion, there is a danger that the

same conclusion might apply to the human mind (iii.). For example,

‘all the arguments used to prove substantial forms can be applied to the

formof a clock, although no one claims that it is substantial’ (iii.). He

returns to this type of argument when he tries to formulate an argument

against substantial forms.

It is clearly unacceptable that any substantial form would begin to exist unless it were

created afresh by God. However, we see every day that many of the forms that are said

to be substantial begin to exist, although the people who think they are substances do

not think that they are created by God. They are therefore mistaken. This is confirmed

in the case of the soul, which is the true substantial form of human beings, because

it is thought to be created immediately by God for no other reason except that it is a

substance. (iii.)

The other reason used by Descartes, which has echoes of his discussion

ten years earlier inThe World, was that, even if substantial forms were

accepted, they would fail completely to provide the kind of explanations

forwhich they were invented by their supporters.

Philosophers had no reason to introduce substantial forms except that, by using them,

they were able to explain the characteristic actions of natural things, of which they

would be the principle or source....But clearly one cannot explain any natural action

bysuch substantial forms, since even their proponents admit that they are occult and

that they do not understand them. For if someone claims that a natural action results

from a substantial form, that is the same as saying that it results from something that

they do not understand, which explains nothing. (iii.)

There is an obvious sense in which the problem raised by Voetius was

insoluble within the terms used by scholastic philosophy. If the soul is

classified as a substance, it compromises the unity of human nature. If,

however, one focuses on the unity of human experience, it is difficult

to understand how this could result from some inexplicable union of

two distinct substances. It was this latter problem that tempted Regius

into describing the relation between mind and body as ‘accidental’. In an

attempt to avoid criticism, Descartes encouraged him to acknowledge the

limits of our understanding, and to admit that he may have misunderstood

technical terms in scholastic philosophy. Above all, he should continue to

press the point that human bodies and souls are joined together by a ‘real

substantial union’, that the resulting union constitutes a ‘single entity in