Most people are rather confident of their ability to recognize bullshit and to avoid being taken in by it, yet we have no clear understanding of what bullshit is, why there is so much of it, or what functions it serves--and we lack a conscientious appreciation of what it means to us. In other words, as Harry Frankfurt writes, "we have no theory." Frankfurt, one of the world's most influential moral philosophers, attempts to build such a theory here. With his characteristic combination of philosophical acuity, psychological insight, and wry humor, he argues that bullshitters misrepresent themselves not as liars do, that is, by deliberately making false claims. Rather, bullshitters seek to convey a certain impression of themselves without being concerned about whether anything at all is true. They quietly change the rules governing the conversation so that claims about truth and falsity are irrelevant. Frankfurt concludes that although bullshit can take many innocent forms, excessive indulgence in it can eventually undermine the practitioner's capacity to tell the truth in a way that lying does not. Liars at least acknowledge that it matters what is true. By virtue of this, Frankfurt writes, bullshit is a greater enemy of the truth than lies are.