  Some of the Sophists classified types of sentences (logoi) according to their force. So Protagoras (485–415 BCE), who included wish, question, answer and command (Diels Kranz (DK) 80.A1, Diogenes Laertius (D. L.) 9.53–4), and Alcidamas (pupil of Gorgias, fl. 4th BCE), who distinguished assertion (phasis), denial (apophasis), question and address (prosagoreusis) (D. L. 9.54). Antisthenes (mid-5th–mid-4th cent.) defined a sentence as ‘that which indicates what a thing was or is’ (D. L. 6.3, DK 45) and stated that someone who says what is speaks truly (DK49). Perhaps the earliest surviving passage on logic is found in the Dissoi Logoi or Double Arguments (DK 90.4, c. 400 BCE). It is evidence for a debate over truth and falsehood. Opposed were the views (i) that truth is a—temporal—property of sentences, and that a sentence is true (when it is said), if and only if things are as the sentence says they are when it is said, and false if they aren’t; and (ii) that truth is an atemporal property of what is said, and that what is said is true if and only if the things are the case, false if they aren’t the case. These are rudimentary formulations of two alternative correspondence theories of truth. The same passage displays awareness of the fact that self-referential use of the truth-predicate can be problematic—an insight also documented by the discovery of the Liar paradox by Eubulides of Miletus (mid-4th c. BCE) shortly thereafter.