 Formal accidental predication is then further divided into secundum motum and secundum habitudinem (De universalibus, pp. 187–88). The basic idea of this last division seems to be that modes of being and natures of the accidental forms determine the set of substantial items which can play the role of their substrate. Penbygull distinguishes between those accidental forms that require a substance capable of undergoing change (per se mobile) as their own direct substrate of inherence, and those which do not need a substrate with such a characteristic. Forms like quantity, whiteness, alteration, diminution and so on belong to the first group, while relations of reason and respectus, like causation, difference, and so on, fall under the second one. The forms of the first group bring about formal accidental predication secundum motum, and the forms of the second group formal accidental predication secundum habitudinem. The former necessarily entail singular substances as their substrates, since individuals alone can undergo change, while the latter can directly inhere in both individual and universal substances (insunt denominative tam communibus quam singularibus—De universalibus, p. 188).