Several specific maxims of English conversation that suggest interpersonal cooperation in the process of communication are applied to conversation in Japanese. The maxims concern implicature, a proposition implied in an utterance in a particular context but not expressly stated. It is proposed that: (1) while it is easy to overstate or exaggerate in American English, the Japanese prefer to understate or remain close to the truth value of quantitative statements; (2) the amount of information that must be specified to make the statement as informative as necessary is less for the Japanese than for Americans; (3) while both American and Japanese speakers constantly adjust communication forms to meet semantic and pragmatic requirements, the pragmatic force carries more importance for selection of utterance type in Japanese than in American English. These three hypotheses, it is argued, account for much of the communication difference in the two cultures and for the common characterization of the Japanese as "inscrutable." Comparisons are drawn from English and Japanese ways of expressing a variety of assertions. (MSE)