Sperber and Wilson propose that the key to a theoretical understanding of communication – and, indeed, of cognition in general – is provided by the notion of relevance. Thus (Sperber and Wilson, 1986c/1991, p. 586):
Our suggestion is that humans tend to pay attention to the most relevant phenomena available; that they tend to construct the most relevant possible representations of these phenomena, and to process them in a context that maximizes their relevance. Relevance, and the maximisation of relevance, is the key to human cognition.
In order to explain the notion of relevance, we need to make clear the idea of a contextthat Sperber and Wilson use. In their theory, a context is (1986a, p. 15) ‘a subset of the hearer’s assumptions about the world’ that provides potential premises to be used in inferences. The idea is that, at any given point in a conversational exchange, the hearer has some assumptions ‘in the forefront of his attention’. When a new proposition is introduced – say, as the result of a communicative act on the part of the speaker – the newly introduced proposition and the pre-existing context interact inferentially, so as to produce contextual effects. An implication that depends on the new proposition and also on some of the assumptions in the context is said to be a contextual implicationof the new proposition: and contextual implication is the simplest example of a contextual effect.
Relevance is a matter of having contextual effects (1986c/1991, p. 586):
We claim that information is relevant if it interacts in a certain way with your existing assumptions about the world.
Roughly, the more contextual effects a proposition has, the more relevant it is. However, the cost of deriving contextual effects has to be taken into account as well. So we add a second condition – namely, that the less effort that is required in order to derive contextual effects from a proposition, the more relevant it is (1986c/1991, p. 587):
(a) Other things being equal, the greater the contextual effects, the greater the relevance.
(b) Other things being equal, the smaller the processing effort, the greater the relevance. (129)
Davies, Martin. “Philosophy of Language.” The Blackwell Companion to Philosophy. Ed. Bunnin, Nicholas and E.P. Tsui-James. Blackwell Publishers, 2001. 129.