Lakhasly

B's "I don't know" is an admission of not being fully able to meet the quality maxim, which is the basis for 'perhaps' in the implicature. The excuse also alerts A not to infer anything from B's not simply giving clear directions to the desired section, which is to say that B seems to offer too small a quantity of information. Relevance is also in play: B talking about psycholinguistics books when A has asked about sociolinguistics books can be taken as co-operative by reasoning that B must think that it could be relevant that books in another long- named branch of linguistics are there; specialist branches of the same subject could have similar names.

B's "I don't know" is an admission of not being fully able to meet the quality maxim, which is the basis for 'perhaps' in the implicature. The excuse also alerts A not to infer anything from B's not simply giving clear directions to the desired section, which is to say that B seems to offer too small a quantity of information. Relevance is also in play: B talking about psycholinguistics books when A has asked about sociolinguistics books can be taken as co-operative by reasoning that B must think that it could be relevant that books in another long- named branch of linguistics are there; specialist branches of the same subject could have similar names.