  Part of the issue rests on the requirement that first principles, which assert primary, indemonstrable attributes of their subjects, be necessary truths. Thomas takes it that they must be strictly necessary, universally true in every case at every time. Albert thinks the necessity involved here is of another sort, a conditional necessity, so that the attribute belongs to its subject necessarily, if nothing prevents it. Thus he can identify an actuality as a primary attribute, allowing that possession of the attribute by the subject only occurs “for the most part,” and still identify the first principle asserting this possession of the attribute as a necessary truth. It seems that Thomas Aquinas was less radically Aristotelian on this point than his master. The metaphysical difference led to a notorious and long-lasting dispute over the nature of the highest sort of demonstration (demonstratio potissima).