All generalizations are false, including this one.This is widely attributed to Twain online, but it undoubtedly isn't by him: the first print attribution to Twain I can find dates to 1973. So who did coin it? Google Books finds the first appearances are in the second decade of the 20th century, with the usual vague attributions, including:
"some one, a Frenchman perhaps" (1911); "the man" (1917); "an old Chinese proverb" (1919); "Dumas" (1920); "a French professor" (1920); "one of my history professors at college" (1921); "the Frenchman" (1922; "the witty epigrammatist" (1923); "the Gallic epigrammatist" (1926); "a witty philosopher" (1927); "the witty writer" (1928).
All that can really be said is that the earliest examples are all in US publications. The repeated attribution to a French origin did look hopeful (see previously, Batrachian breakfasts), but the French form - "Toutes les généralisations sont fausses, y compris celle-ci" - appears no older, nor any better attributed, than the English version.
I have, however, found a more detailed scenario for a different wording:
I would recall what happened in a debate of the French Chamber of Deputies. A deputy, criticising the previous speaker, said: "Monsieur X has generalized too freely. I contend that all generalizations are wrong" — and here he paused, and his Gallic wit saved him, when he added — "Yes, all generalizations are wrong, even this one."Currently, the trail ends there.
- The Asiatic Review, Volume 24, The East India Association, 1928.
Addendum: 10 April 2014. I just pushed back the date a little, though with attributions no more likely to be true:
Voltaire has said, "All generalizations are false, and this is no exception."The bulk of attributions, nevertheless, claim a French origin.
- Engineering News, Vol 1, No. 26, page 366, 1903
.... as a Frenchman brilliantly said, “All generalities are false, this one included"
- The Blue and Gold, Volume 20, page 179, 1893