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....