 But even further problems arose from considering the identity or distinctness of the individualized natures signified by several common terms in one and the same individual. The metaphysical debate over the real distinction of essence and existence from this point of view is nothing but the issue whether the individualized common nature signified by the definition of a thing is the same as the act of being signified by the verb ‘is’ in the same thing. In fact, the famous problem of the plurality vs. unity of substantial forms may also be regarded as a dispute over whether the common natures signified by the substantial predicates on the Porphyrian tree in the category of substance are distinct or the same in the same individual (cf. Callus 1967). Finally, and this appears to be the primary motivation for Ockham’s innovations, there was the question whether one must regard all individualized common natures signified in the same individual by several predicates in the ten Aristotelian categories as distinct from one another. For the affirmative answer would involve commitment to a virtually limitless multiplication of entities.