AbstractIn Mandarin conversation, utterances about future actions with severe consequences are observed to correlate with bigger promises, marked by devices indicating greater illocutionary force, as compared with those about actions with less serious consequences. Applying the principle of proportionality proposed byGoffman (1971), I argue that participants’ design of promise is proportional to the severity of the action consequences, which is evaluated by the participants on a moment-by-moment basis. The ad hoc construction of promises shows that promising is a dynamic process, rather than a one-time action. The proportionality principle may also account for the differences between promises in institutional discourse and ordinary conversation.