Assertion, a speech act whereby the speaker puts forward a proposition as true or, secondarily, the proposition affirmed in such an act. The main vehicle for making assertions is the declarative sentence, spoken or written. Assertion is the default value of a declarative utterance or inscription. Assertion's conjugate is questioning. A question is a prompt to assertion, and a correct assertion answers the question. The point of assertion is persuasion, and if all goes well, by asserting that P, you persuade your audience that P. Assertion is fundamental to human social life. It is the primary means by which we share our knowledge with others. It is critical to planning and coordinating behavior. There are clear antecedents of assertion in non-human animals, viz. signalling behavior, but it is controversial whether such forms of communication count as genuine assertions. Some argue that assertion occurs only when appropriate conventions are antecedently in place. For example, perhaps the declarative mood is a convention in virtue of which we are able to assert. Assertions have a word-to-world direction of fit: if the world isn't the way the assertion says it is, then the assertion is false and therefore bad qua assertion. But this is true of other common speech acts too. Guesses, conjectures, hypotheses, predictions, and guarantees all have a word-to-world direction of fit too. What individuates assertion within this group? The best answer is that assertion is individuated normatively and its norm is knowledge. On this view, known as the knowledge account of assertion, the speech act 1 | 2 of assertion is constituted by a rule which enjoins us to assert P only if we know that P is true. The best evidence for the knowledge account of assertion is an explanatory argument from linguistic patterns. Everywhere we look, assertion and knowledge are linked. A natural way to get someone to tell you whether P is to ask, 'Do you know whether P?'. Ordinarily an appropriate response to an assertion is to ask, 'How do you know?'. And a natural way to avoid answering a direct question is to say, 'Sorry, I don't know the answer.' Word count: 351 John Turri john.turri@gmail.com