to behave according to the maxims. So, when a speaker appears to have violated a maxim by saying or making as if to say something that is false, uninformative or too informative, irrelevant, or unclear, the assumption that the speaker is in fact obeying the maxims causes the interpreter to infer a hypothesis about what the speaker really meant. That an interpreter will reliably do this allows speakers to intentionally "flout" the maxims—i.e., create the appearance of breaking the maxims in a way that is obvious to both speaker and interpreter—to get their implicatures across. Perhaps Grice's best-known example of conversational implicature is the case of the reference letter, a "quantity implicature" (i.e., because it involves flouting the first maxim of Quantity): A is writing a testimonial about a pupil who is a candidate for a philosophy job, and his letter reads as follows: "Dear Sir, Mr. X's command of English is excellent, and his attendance at tutorials has been regular. Yours, etc." (Gloss: A cannot be opting out, since if he wished to be uncooperative, why write at all? He cannot be unable, through ignorance, to say more, since the man is his pupil; moreover, he knows that more information than this is wanted. He must, therefore, be wishing to impart information that he is reluctant to write down. This supposition is tenable only if he thinks Mr. X is no good at philosophy. This, then, is what he is implicating.) Given that a speaker means a given proposition p by a given utterance, Grice suggests several features which p must possess to count as a conversational implicature. Nondetachability: "The implicature is nondetachable insofar as it is not possible to find another way of saying the same thing (or approximately the same thing) which simply lacks the implicature." Cancelability: "...a putative conversational implicature is explicitly cancelable if, to the form of words the utterance of which putatively implicates that p, it is admissible to add but not p, or I do not mean to imply that p, and it is contextually cancelable if one can find situations in which the utterance of the form of words would simply not carry the implicature." Non-Conventionality: "...conversational implicata are not part of the meaning of the expressions to the employment of which they attach." Calculability: "The presence of a conversational implicature must be capable of being worked out; for even if it