Taking knowledge as a starting point › Why Assertion Carries a Commitment

Chapter 11 proposes that assertion has a knowledge rule: assert a proposition only if you know it. Assertion is the act of putting something forward as true. The rule is a proposed constitutive standard for that act, rather than a claim that speakers always obey it. The chapter abstract and section list distinguish the knowledge account from accounts requiring only truth or reasonable belief.

Our report example separates those standards. A person who confidently guesses that submission succeeded might tell the truth without knowing it. If asked for a basis, admitting that it was a guess changes how the listener should use the answer. A qualified prediction, an explicit supposition, and an unqualified assurance make different contributions to a conversation. The knowledge rule helps explain why those differences matter.

The rule supplies a necessary condition, not a complete permission to speak. Knowing a private fact does not settle whether disclosing it would be considerate or lawful. Conversely, a sincere mistake can violate a standard without making the speaker dishonest or deserving severe blame. These distinctions prevent an epistemic account of assertion from becoming an indiscriminate moral verdict on every mistaken sentence.

A lottery sharpens the issue. Knowing that one ticket has a very low chance of winning seems different from knowing that it will lose. Williamson uses lottery cases in arguing against weaker assertion rules. The relevant contrast is between a probability claim and an outright claim about the outcome, rather than between a mathematical probability of one and every other probability. His account does not replace ordinary knowledge with absolute certainty.