Although Thomas Aquinas assumes that all knowledge begins in the senses, he maintains that substantial forms and the essences of material things are not apparent to the senses. Clearly, the noetic of abstraction per se cannot account for our knowledge of them. Thomas often says that they are “unknown in themselves” but “become known” through their accidents. The author argues that properties, or proper accidents — namely, accidents that are interconvertible with a subject — play a crucial role in this (...) obscure area of Thomas’s thought. Beginning with an examination of the property in logic , the author goes on to examine Thomas’s accounts of heat as a property of fire, and the powers of the soul as properties of its essence. Thomas maintains that such properties flow from the essence by a causal relation that he calls resultatio, but that their coexistence with the essence is absolutely necessary in a quasi-logical manner . Finally, the author suggests that in Thomas’s view, accidents really do make the hidden quiddities of their subjects known: knowing created things through their accidents is not at all like knowing God through creatures. (shrink)