On the rationality of 'relevance' and the relevance of 'rationality'

Sperber and Wilson's attempt to replace the Gricean CP and its maxims by a general Principle of Relevance from which all the other maxims follow is shown not to be entirely satisfactory without further modifications, since it makes the wrong predictions with respect to such instances as justification of speech acts, and counter-intuitive claims in cases of redundancy. An alternative offered by Kasher, whereby the various maxims of the CP follow from some major Rationality Principle, is shown to be required alongside and not in place of the Principle of Relevance. In addition, reference is shown to be required to such independently attested reasoning principles as establishing causal relations, presumably, as part of the heuristics for the retrieval of the relevant piece of stored knowledge in a particular instance involving comprehension.