Grice’s analysis of conversational implicatures implies that they will have certain properties which allow us to distinguish them from other kinds of inference. We have already mentioned the most important of these, namely the fact that they are defeasible. This term means that the inference can be cancelled by adding an additional premise. For example, conversational implicatures can be explicitly negated or denied without giving rise to anomaly or contradiction, as illustrated in (17). This makes them quite different from entailments, as seen in (18).
(17) a. Dear Sir, Mr. X’s command of English is excellent, and his attendance at tutorials has been regular. And, needless to say, he is highly competent in philosophy. Yours, etc.
b. He has been paying a lot of visits to New York lately, but I don’t think he has a girlfriend there, either.
c. John has most of the documents; in fact, he has all of them.
(18) John killed the wasp (#but the wasp did not die).
A closely related property is that conversational implicatures are suspendable:9 the speaker may explicitly choose not to commit to the truth or falsehood of the inference, without giving rise to anomaly or contradiction. This is illustrated in (19a). Again, the opposite is true for entailments, as seen in (19b).
(19) a. The water must be warm by now, if not boiling.
b. # The water must be warm by now, if not cold.
Conversational implicatures are calculable, that is, capable of being worked out on the basis of (i) the literal meaning of the utterance, (ii) the Cooperative Principle and its maxims, (iii) the context of the utterance, (iv) background knowledge, and (v) the assumption that (i)–(iv) are available to both participants of the exchange and that they are both aware of this. However, conversational implicatures are also indeterminate: sometimes multiple interpretations are possible for a given utterance in a particular context.
Because conversational implicatures are not part of the conventional meaning of the linguistic expression, and because they are triggered by the semantic content of what is said rather than its linguistic form, replacing words with synonyms, or a sentence with its paraphrase as in (20), will generally not change the conversational implicatures that are generated, assuming the context is identical. Grice used the somewhat obscure term nondetachable to identify this property. He explicitly notes that implicatures involving the maxim of Manner are exceptions to this generalization, since in those cases it is precisely the speaker’s choice of linguistic form which triggers the implicature.10
(20) A: Smith doesn’t seem to have a girlfriend these days.
B1: He has been paying a lot of visits to New York lately.
B2: He travels to New York quite frequently, I have noticed.
Sadock (1978: 294) noted another useful diagnostic property, namely that conversational implicatures are reinforceable. He used this term to mean that the implicature can be overtly stated without creating a sense of anomalous redundancy (21a–b). This is another respect in which conversational implicatures differ from entailments (21c).
(21) a. John is a capable fellow, but I wouldn’t call him a genius.
b. Some of the boys went to the soccer match, but not all.
c. ?*Some of the boys went to the soccer match, but not none.
9 Horn (1972); Sadock (1978).
10 Grice (1975: 58).
