 Even though Aristotle did not define modal terms with the help of extensional notions, examples of this way of thinking can be found in his discussion of eternal beings, the natures of things, the types of events, and generic statements about such things. (See, for example, Metaphysics. IX.10.) Modal terms refer to the one and only world of ours and classify the types of things and events on the basis of their actuality. This paradigm suggests that actualization is the general criterion of the genuineness of possibilities, but the deterministic implications of this view compelled Aristotle to seek ways of speaking about unrealized singular possibilities. Diodorus Chronus (fl. 300 BCE) was a determinist who found no problem in this way of thinking. Some commentators have argued that Aristotle’s views showing similarities to the statistical model are based on special metaphysical and ontological doctrines and not on his understanding of modal terms themselves. However, it is not clear that Aristotle had any such distinction in mind. (For different interpretations and evaluations of the role of this model in Aristotle, see Hintikka 1973, Sorabji 1980, Seel 1982, Waterlow 1982a, van Rijen 1989, Gaskin 1995.) In Posterior Analytics I.6, Aristotle states that certain predicates may belong to their subjects at all times without belonging to them necessarily. Some ancient commentators took this to mean that Aristotle operated with a distinction between strong essential per se necessities and weak accidental necessities in the sense of non-essential invariances, such as inseparable accidents (see also Porphyry, Isagoge 3.5–6), and that this distinction played an important role in his modal syllogistic. See the commentaries on the Prior Analytics by Alexander of Aphrodisias (36.25–32; 201.21–24) and Philoponus (43.8–18; 126.7–29); Flannery 1995, 62–65, 99–106. This was also the view of Averroes and some Latin authors in the Middle Ages. (See below, section 3.)