In his discussions of the various readings of modal propositions, Ibn Sīnā’s focus is mostly on a distinction which was later labelled the distinction between descriptional (waṣfī) and substantial (ḏātī) readings of a modal proposition. Given that for Ibn Sīnā all categorical propositions are either implicitly or explicitly modal, the substantial–descriptional distinction is in some sense applicable to the readings of all categorical propositions. This distinction is based on how (i.e., under which conditions) the predicate of a categorical proposition is true of its subject. According to the substantial reading, the predicate is true of the subject (perhaps with a certain alethic or temporal modality) as long as the substance of the subject exists. On the other hand, according to the descriptional reading, the predicate is true of the subject (again, perhaps with a certain modality) as long as the substance of the subject is truly described by the subject. To be clearer, consider the following proposition:(1) Every S is P. The difference between the substantial and descriptional readings of (1) can be articulated as follows:Substantial Reading of (1): Every S, as long as it exists, is P.Descriptional Reading of (1): Every S, as long as it is S, is P.It is in principle possible that a proposition is true on one of these readings and false on the other. It is only the context which determines how a proposition must be read to be true. To give an example, consider the following proposition:(2) Every bachelor is unmarried. The substantial and descriptional readings of (2) are respectively as follows: (3) Every bachelor, as long as he exists, is unmarried.(4) Every bachelor, as long as he is bachelor, is unmarried.These two propositions have different truth values. Contrary to (3)—which is false—(4) is true. This is because a bachelor is unmarried only insofar as he is described as a bachelor. So (4) is true. By contrast, it is in principle possible for a person who is a bachelor in some period(s) of time to be ...