When an action stretches over time, like standing or sitting, usage is unproblematic. But when an action is more punctate, like swatting a fly or having sex, present tense refers to a span of time in which the event is habitual or repeated. If I say ''John is swatting flies,'' he doesn't have to land a blow at the instant the words come out of my mouth. Mr. Starr's lawyers accused Mr. Clinton of pedantically restricting ''there is sex'' to coitus when the President gave his deposition. Mr. Clinton had a point when he replied that the present tense can refer to a span of time over which acts tend to be repeated, and at that point he and Ms. Lewinsky had broken up and were unlikely to have sex again.
Conversation requires cooperation.
Listeners assume speakers are conveying information relevant to what they already know and what they want to know. That allows them hear between the lines in order to pin down the meanings of vague or ambiguous words and to fill in the unsaid logical steps. The reason we cannot converse with our computers is not that the engineers cannot program in the grammar and vocabulary of the English language, but that they cannot program in the common sense of a human speaker. In the old ''Get Smart'' television series, Maxwell Smart asks the robot Hymie to ''give me a hand,'' and Hymie proceeds to unscrew his hand and hold it out. Mr. Clinton, of course, is not trying to impersonate Hymie.