  Ockham agreed with Scotus and Aquinas that the definition of the subject is the middle term in a demonstration of the highest sort, but he is no more comfortable with the notion that the subject somehow efficiently causes an attribute in itself through its essence than is Albert. Indeed, he insists that nothing of interest follows for a demonstration from the real definition of a subject giving its genus and difference. This is because what follows demonstratively follows on some real structure of really distinct parts within the subject. This means, first of all, that a genus-difference definition of a thing, which does not identify really distinct parts in it, cannot serve as a middle term in demonstration. Moreover, since God has no real parts, but is perfectly simple, no demonstration concerning God can be constructed at all. But some definitions of a subject do identify real parts within it. One case occurs in mathematics, in which the real definition of a subject obliquely conveys parts of the subject, for instance, as in the definition of a triangle, which is not said directly to be identical to its parts, the lines making it up, say, but is said obliquely to be something composed from those lines.  This, for Ockham, is the only possibility for the highest sort of demonstration (Summa Logicae III.II 40). It alone meets Thomas's criterion for such a demonstration, i.e. it shows the attribute to belong actually to the subject necessarily and in every case, Albert's criterion, that the attribute be occurrent and not merely a capacity, and Giles's requirement that the attribute be really distinct from the subject, so that it can reasonably be said that the conclusion is not an immediate proposition. In another case, one can demonstrate an implicitly negative attribute of something from the fact that it is composed of real parts, arguing, for instance, that “Whatever has separable parts is destructible, every material thing has separable parts, therefore every material thing is destructible.” This, however, since it shows an attribute which conveys the parts of the subject negatively, is not a demonstration of the highest sort.