A serious and good philosophical work could be written consisting entirely of jokes.

Ludwig Wittgenstein (1889-1951) Austrian-English philosopher

Quoted in Norman Malcolm, Ludwig Wittgenstein: A Memoir (1958)
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This is usually presented as a direct quotation, but is perhaps a paraphrase. The full passage from Malcolm:

It is worth noting that Wittgenstein once said that a serious and good philosophical work could be written that would consist entirely of jokes (without being facetious).