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On Bullshit (1986), by philosopher Harry G. Frankfurt, is a philosophy essay that presents a theory of bullshit that defines the concept and analyses the applications of bullshit in the contexts of communication. It was first published in a journal in 1986, but only became well known when republished as a booklet in 2005.

Frankfurt argues that bullshit either can be true or can be false; hence, the bullshitter is a man or a woman whose principal aim — when uttering or publishing bullshit — is to impress the listener and the reader with words that communicate an impression favorable to the speaker, with no concern for the truth of what they're saying. Likewise, the bullshitter is not concerned with consistency between what they're saying at the moment, and anything they've previously said. Consequently, “the bullshitter is faking things, but that does not necessarily mean he gets them wrong.” He simply doesn't care. In contrast, the liar must know the truth, of the matter under discussion, in order to better conceal it from the listener or the reader being deceived with a lie; while the bullshitter’s sole concern is personal advancement and advantage to his or her agenda; bullshit thus is a greater enemy of the truth than are lies