  are said to exhibit modality de dicto (roughly, modality  of the proposition).  Possible world semantics provides an illuminating analysis of the key difference between the two: The truth conditions for both modalities  involve a commitment to possible worlds; however, the truth  conditions for sentences exhibiting modality de re involve in  addition a commitment to the meaningfulness of   transworld identity,  the thesis that, necessarily, every individual (typically, at any  rate) exists and exemplifies (often very different) properties in  many different possible worlds. More specifically, basic possible  world semantics yields intuitively correct truth values for sentences of the latter sort by (i) permitting world domains to overlap and  (ii) assigning intensions to predicates, thereby, in effect,  relativizing predicate extensions to worlds. In this way, one and the same individual can be in the extension of a given predicate at all  worlds in which they exist, at some such worlds only, or at none at  all. (For further discussion, see the entry on  essential vs. accidental properties.)  