Standard implementations of Grice’s theory of conversational implicature assume that the derivation an implicature always begins with a single proposition expressed by means of a sentence in a given context. Against this received view, I argue that, in at least three ways, implicatures are discourse-based rather than proposition-based. First, in some cases an implicature can only be derived fro...

The standard dictionary definition of a formally valid argument in classical, bivalent, deductive logic proceeds as follows: An argument is valid if it is impossible for all its premises to be true and its conclusion to be false. A valid argument, unlike a sound one, can have false premises or it can have a mixture of true and false premises, but if all of its premises are true, then its conclu...