Entailment vs. Implicature

An entailment is an inference that necessarily holds given the truth of a statement. An implicature is an inference drawn from the specific context in which a statement is made, one that may be canceled. The contrast between the two is a foundational distinction in the study of meaning.

Entailments

If the bear escaped from the zoo is true, several inferences necessarily follow. It follows that the bear escaped, that an animal escaped from the zoo, and that the bear moved. Each holds by necessity: escape entails movement in location, so the bear must have moved; being a bear entails being an animal, so an animal must have escaped. These inferences cannot fail if the original statement is true.

Implicatures

Other inferences arise without holding necessarily. Suppose someone asks, "What escaped from the zoo?" and the reply is the bear escaped from the zoo. The questioner will infer that a lion did not escape, even though the sentence does not mean that. The inference arises because the questioner assumes that if a lion had also escaped, the speaker would have said so.

This inference is cancellable. The speaker can continue, "The bear escaped from the zoo, and in fact a lion escaped also," without contradiction. Conversational implicatures of this kind are context-dependent, and their cancellability is exactly what separates them from entailments, which cannot be canceled. There are several kinds of implicature, and the topic grows far more complex, but this core distinction is stable.

Semantics and Pragmatics

The line between entailment and implicature traditionally marks the divide between semantics and pragmatics. Both deal with meaning. Semantics handles entailments, that is, truth-conditional meaning. Pragmatics handles meanings that are not truth-conditional and not entailed, the implicated and more context-dependent meanings. The boundary has been challenged and there is much more to it, but it remains a good starting point.