Appendix 32.

(895) [Tradition and the subjectivity of sensations]

Some believe that before Descartes the subjectivity of sensation had never been observed, but it was familiar to all antiquity. In fact the sophists misused it by denying every truth except what is subjective or relative to the human being. In this way they created a universal scepticism. The sceptics were followed by the epicureans. Lucretius, for example, denied colour to first bodies, that is, to corporeal essence:

Similarly, he denies cold, heat, sound, odour and taste:

He proves this with beautiful observations (2, 729-863).

The tradition of this truth was not lost when Scholasticism flourished. St. Thomas expressly teaches that the phrase, 'The sun is hot', must not be understand to mean that we attribute the sensation of heat to the sun, but to mean that the sun is the cause of this sensation. It has the same sense as 'Medicine is healthy', that is, medicine contains neither health nor illness but causes health in us (C. Gent., I, qq. 29 and 31). This teaching of St. Thomas stamps the two periods of scholastic philosophy: the first, brilliant period, when Aquinas and other sublime minds flourished; the second, final period, when Scholasticism, like all human things, declined. Providence then placed the promotion of philosophical truth in other hands. It was Galileo who restored the truth we are discussing, and a quotation from his fine words will be helpful:

I do not think that external bodies require anything more than size, shape, number and movement (slow or rapid) to stimulate taste, odour and sound. If we remove ears, tongue and nose, I am certain that shape, number and movement remain but not odour, taste and sound which, outside a living animal, are simply words, just as tickling and titillation are mere names when the armpits and the skin around the nose are removed (where tickling is initiated by touch).

He applies the same teaching to heat:

I am very much of the opinion that heat is of this kind. The things which produce and make us feel heat and are generally called 'fire', are a quantity of very tiny particles of a particular shape which move at a particular speed. They are so fine that when they strike our body, they penetrate it and, as they pass through and touch our substance, we feel them. This feeling is the experience we call heat, pleasant or unpleasant according to their number and the relative speed with which the particles penetrate us. This penetration is pleasant when it helps our insensible, necessary perspiration, but unpleasant when it causes too great a division and disruption of our substance. In short, the action of fire is simply the movement by which it penetrates all bodies with its estreme fineness. It breaks the bodies down slowly or rapidly, depending on the number and speed of the fiery particles and on the degree of density of the bodies' matter. Most of these disintegrating bodies change into other fiery particles and continue the dissolution as long as they encounter dissoluble matter. But I do not think that in fire there is any other quality which may be warm. Only shape, number, movement, penetration and touch are present. In other words, fire is such a part of ourselves that if the animated, sensitive body is removed, heat is nothing more than a word.