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In De operationibus occultis naturae, Thomas Aquinas explains the notion of occult properties arising from the specific forms of inanimate things, which accounts for phenomena that cannot be explained by the mere arrangement of primary qualities, in accordance with a philosophical and medical framework partly inherited from Galen and Avicenna. For Thomas, these properties are only one level in a hierarchically ordered array of beings defined by the hylemorphic union and crowned by man, whose substantial form is the soul. One finds parallels to this construction in Albert the Great’s De mineralibus. Other occurrences in Thomas Aquinas’works, where the magnet endowed with an attractive property is compared to man endowed with a soul, allow us to better understand why Thomas Aquinas accepts specific or substantial occult properties, but rejects individual or accidental occult properties.