Descartes: A Biography

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 Descartes: A Biography

the observed evidence to confirm the hypothetical explanation. Descartes

explains why this is merely an appearance of circularity by distinguishing

betweenprovingandexplaining.

Yo ualso say that ‘to prove effects by a cause, and then to prove this cause by the same

effects, is a logical circle’. I hold the same. However, I do not accept, for that reason,

that it is a logical circle to explain effects by a cause and then to prove the cause by

the effects, because there is a big difference between ‘to prove’ and ‘to explain’. I add

that it is possible to use the word ‘demonstrate’ to mean one or the other, at least if

oneunderstands it according to common usage and not with the special meaning that

philosophers give it. (ii.–)

In a word, there is no vicious circle involved because the relations between

hypothetical causes and observed effects are more complicated than they

initially appear. The effects are known by observation or experience, and

the fact that we know these is usedto confirmthe hypothetical cause that

weinvent or construct. Once the cause is in place, there is no suggestion

that it is used to confirm the truth of the effects. That would certainly be

circular. The hypothetical causeexplainsthe effect.

Avoiding circularity was the easier of the two problems identified by

Morin. The real challenge was to avoid committing a fallacy by claiming

that the success of a given explanation confirms the truth of its assump-

tions. Here Descartes appealed to the fact that he explained so many effects

with so few causes that the very simplicity of his theory helped to confirm

it. ‘It is not always as easy to adjust one single cause to many different

effects unless it is the true cause from which they result’ (ii.).

The other line of defence was to compare the mechanical models on

which Descartes relied to the vast profusion of special entities invented

bytraditional philosophy.

If one compares the assumptions of other philosophers with mine – that is, all their ‘real

qualities’, their ‘substantial forms’, their ‘elements’ and similar things, the number of

which is almost infinite – with this one assumption, that all bodies are composed of

various parts (something that can be observed with the naked eye in some cases and

can be proved by an infinity of arguments in the others)...and if one compares what

Ihavededuced from my assumptions concerning vision, salt, the winds, the clouds,

snow, thunder, the rainbow, and similar things, with what others have derived from

theirs about the same phenomena, I hope that this will be enough to persuade those

who are not too prejudiced that the effects that I explain have no other causes apart

from those from which I deduced them. (ii.)