It occurred when Clinton, on January 17, 1998, in the course of his grand jury testimony for Kenneth W. Starr’s expanded Whitewater investigation, said: “It depends on what the meaning of the word ‘is’ is.” He was answering a question as to whether he wasn’t lying when, earlier, he assured one of his top aids that “there’s nothing going on between us,” i.e., Clinton and erstwhile White House intern Monica Lewinsky, or when he told PBS newscaster Jim Lehrer that “there is no improper relationship” between Lewinsky and him.

Now, logicians distinguish three "modes" of the word “is”: the existential, the predicative, and the “is” of identity. One can say of something that it is in the sense that it exists, such as when the believer asserts that “God is” (existential). Or one can say of something that it possesses a certain property, as when the geologist states that a particular rock is reddish, light, and porous (predicative). Finally, one can say of something that it is the same as x, as when the astronomer says that Venus is the morning star or Lois Lane says that Clark Kent is Superman (identity).

But these distinctions are not what Clinton had in mind. He was concerned with the grammar of “is,” specifically its indication of the present tense and the fact that since, by the time he made his statements about Lewinsky, their sexual relationship had ended, what he said, given that it referred to the present, was strictly true. Clearly, Clinton did not say: “There was no improper relationship.” He even went so far as to implicitly admit that “if 'is' means is and never has been,” then he had lied. But, of course, as a matter of grammar, “is” doesn’t behave that way. Whether considered as simple present, active or passive, or present progressive, active or passive, Clinton’s denial that there “is” an improper relationship was, when he issued it, by all accounts true.

Even though what mattered to Clinton, so far as “is” was concerned, was grammar not modality, it’s nonetheless worth noting that the mode of “is” in question was existential. The issue was whether a sexual relationship between Lewinsky and Clinton is, whether such a relationship exists or is non-existent and by extension the question of what it means that things are, that there is something rather than nothing. And that is precisely the question that Heidegger attempts to re-assert beginning with "Sein und Zeit" (1927): the question of the meaning of being, the significance of the fact, which is more than one fact among others, that quite apart from their properties and identities, their characteristics and behavior, their origins, causes, effects, and purposes, their structures and functions, things just are.

True, Clinton raised the issue in a regrettably tawdry context, and neglected to develop it very far, but he did raise it. It is to be hoped that, among the projects of Clinton’s presidential library, some consideration is being given to furthering his legacy as a thinker of the relationship between being, or isness, and language by supporting further inquiry into these questions.