  In 1952 P. F. Strawson proposed a logic of presuppositions. It is an
interpretation of Aristotelian logic, i.e. of the logic of the traditional
syllogism. In 1981 Richard Diaz published a monograph in which he presented
truth-relevant logic. This paper shows that truth-relevant logic is but a
propositional version of the logic of presuppositions. A semantics of the logic
of presuppositions is developed using truth-relevant logic. The semantics is
then further extended to polyadic logic and some consequences discussed.
