Descartes: A Biography

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The Principles of Philosophy() 

qualities of bodies, to be as incomprehensible: and therefore could not with reason

presse him, to show how a body was able to doe such an operation, as I should inferre

must of necessity proceede from a spirit, since that neyther could I give account how

the loadestone drew iron, or looked to the north, how a stone, and other heavy thinges

were carried downewardes: how sight or fantasie was made; how digestion or purging

were effected; and many other such questions, which are so slightly resolved in the

schooles.

The obvious danger in this approach to explanation is spelled out in

the Preface to the second treatise (on the soul). Scholastic philosophers,

according to Digby, had turned ‘all bodies into spirits, making (for exam-

ple) heate, or cold, to be of it selfe indivisible, a thing by it selfe, whose

nature is not conceivable’.Having thus collapsed the fundamental dis-

tinction between matter and spirit by using ‘spiritual’ explanations of

merely material phenomena, they risked supporting those who argue from

the same mistake to the opposite conclusion. If purely material things are

mistakenly given a spiritual explanation, then those features of human

experience, such as thought, that require a similar spiritual explanation

are likely to be no more than complex material processes that are not

currently understood.

Digby, in opposition to scholastic philosophy, was anxious to show that

‘our Soule is a substance, and Immortall’.Although in natural philos-

ophy we should rely on the evidence of our senses and avoid postulat-

ing unnecessary forms or substances, the opposite applies here. ‘We are

now out of the boundes that experience hath any iurisdiction over:...we

must in all our searches and conclusions rely only upon the single evi-

dence of Reason.’One of the arguments he used was borrowed from

‘Monsieur des Cartes in his Methode’.This was the argument that

the mind by definition does not have the properties that are characteris-

tic of material things. By appealing to an experience that was relatively

familiar to soldiers at the time, Digby reminds readers that even if one

is missing a leg or an arm, one is still a ‘thinking thing’.Descartes and

Digby both knew that a similar argument does not work in the case of

the brain; without a brain, one ceases to think. Their argument showed

only that arms or legs are not necessary for thinking, while a brain is obvi-

ously necessary. However, they supported their position by arguing that

it makes no sense to think of half a mind, whereas it always makes sense

to think of half a body. The fragility of the argument was beginning to

be exposed.