  Some Platonic dialogues contain passages whose topic is indubitably logic. In the Sophist, Plato analyzes simple statements as containing a verb (rhêma), which indicates action, and a noun(onoma), which indicates the agent (Soph. 261e–262a). Anticipating the modern distinction of logical types, he argues that neither a series of nouns nor a series of verbs can combine into a statement (Soph. 262a–d). Plato also divorces syntax (‘what is a statement?’) from semantics (‘when is it true?’). Something (e.g. ‘Theaetetus is sitting’) is a statement if it both succeeds in specifying a subject and says something about this subject. Plato thus determines subject and predicate as relational elements in a statement and excludes as statements subject-predicate combinations containing empty subject expressions. Something is a true statement if with reference to its subject (Theaetetus) it says of what is (e.g. sitting) that it is. Something is a false statement if with reference to its subject it says of something other than what is (e.g. flying), that it is. Here Plato produces a sketch of a deflationist theory of truth (Soph. 262e–263d; cf. Crat. 385b). He also distinguished negations from affirmations and took the negation particle to have narrow scope: it negates the predicate, not the whole sentence (Soph. 257b–c). There are many passages in Plato where he struggles to explain certain logical relations: for example his theory that things participate in Forms corresponds to a rudimentary theory of predication; in the Sophist and elsewhere he grapples with the class relations of exclusion, union and co-extension; also with the difference between the ‘is’ of predication (being) and the ‘is’ of identity (sameness); and in Republic 4, 436bff., he anticipates the law of non-contradiction. But his explications of these logical questions are cast in metaphysical terms, and so can at most be regarded as proto-logical.