 These semantic rules are motivated by supervaluation logic (van Fraassen 1969; Priest 2001: ch. 7). A sentence is true if and only if it is true in every admissible structure. It is false, by contrast, if and only if it is false in every admissible structure. And a sentence does not have a determinate truth value if and only if it is true in, at least, one admissible structure and false in, at least, another structure that is also admissible.