When we characterize talk as hot air, we mean that what comes out of the speaker’s mouth is only that. It is mere vapor. His speech is empty, without substance or content. His use of language, accordingly, does not contribute to the purpose it purports to serve. No more information is communicated than if the speaker had merely exhaled. There are similarities between hot air and excrement, incidentally, which make hot air seem an especially suitable equivalent for bullshit. Just as hot air is speech that has been emptied of all informative content, so excrement is matter from which everything nutritive has been removed. Excrement may be regarded as the corpse of nourishment, what remains when the vital elements of food have been exhausted. In this respect, excrement is a representation of death that we ourselves produce and that, indeed, we cannot help producing in the very process of maintaining our lives. Perhaps it is for making death so intimate that we find excrement so repulsive. In any event, it cannot serve the purposes of sustenance, any more than hot air can serve those of communication.

— Harry G. Frankfurt, On Bullshit