Development Of The Human Soul

Appendix 1. (792).

As far as I can see, ancient philosophers did not distinguish between general, indeterminate extension which pertains to first matter, and determined extension or extended quantity which does not. This is how St. Thomas explains one of Plato's teachings: 'Quantity and quality, the first accidents to flow from substance, are co-related to the two essential principles of substance, that is, form and matter. QUANTITY CORRESPONDS TO MATTER, which explains why Plato posited "great" and "small" amongst the differences pertaining to matter, and quality to form' (In IV Sent., d. 12, q. 1, art. 1, ad 1). It is fairly easy to understand why St. Thomas says that these entities are accidents consequent upon substance, rather than essential to its constitution, if we remember that the concept or essence of substance is one thing, its realisation another. Quantity, which is determined extension, does not form part of the essence of substance, and in particular of matter, until it is realised with the quantity determined by the will of the Creator. Determined extension or quantity is, therefore, dependent on the extent of the realisation of matter.

This also explains the truth of the statement: 'Measured quantity, although not depending on sensible matter for its explanation, does depend on it for its being. Hence, in predication and in subjection, it takes up the mode of substance and accident. We say, therefore, that a line has quantity because etc.' (ibid., ad 2). 'For its explanation' means 'according to its concept, according to its essence', because quantity can be thought in abstraction from sensible matter, or rather sensible matter can be thought without quantity - the idea of matter does not contain any determinate quantity of this matter. But 'for its being', that is, according to its realisation, it does depend upon sensible matter because quantity is a mode of matter. The opposite is said of matter in its concept, where no quantity is assigned. When matter is realised, however, it must receive a certain quantity according to the decision of whoever realises it. I conclude that extensive quantity does not come forth either from matter, or from the form of bodies, but from their reality which, in turn, comes from the will of the Creator.