Full Idea
Bodies are those substances in which one finds three dimensions.
Gist of Idea
Bodies are three-dimensional substances
Source
Thomas Aquinas (Summa Theologicae [1265], Ia Q18.2c), quoted by Robert Pasnau - Metaphysical Themes 1274-1671 16.2
Book Reference
Pasnau,Robert: 'Metaphysical Themes 1274-1671' [OUP 2011], p.324
A Reaction
Pasnau points out that this extensional view of physical bodies was a commonplace long before Descartes. Presumably there are also non-dimensional substances (such as angels?).