Actual source: A letter to The Economist (16 January 1971), written by one M.J. Shields (or M.J. Yilz, by the end of the letter). The letter is quoted in full in one of Willard Espy's Words at Play books. This was a modified version of a piece "Meihem in ce Klasrum", published in the September 1946 issue of Astounding Science Fiction magazine. http://www.spellingsociety.org/journals/j31/satires.php
Misattributed
Mark Twain: Zitate auf Englisch (seite 23)
Mark Twain war US-amerikanischer Schriftsteller. Zitate auf Englisch.“Be careful about reading health books. You may die of a misprint.”
Attributed to Markus Herz by Ernst von Feuchtersleben, Zur Diätetik der Seele (1841), p. 95 http://books.google.com/books?id=FLc6AAAAcAAJ&pg=PA95&dq=%22Lieber+Freund+Sie+werden+noch+einmal+an+einem+Druckfehler+sterben%22. First attributed to Twain in 1980s, as in The 637 best things anybody ever said, (1982), Robert Byrne, Atheneum. See talk page for more info.
Misattributed
Variante: Be careful about reading health books. You may die of a misprint.
“We believe that out of the public school grows the greatness of a nation.”
Address at a meeting of the Berkeley Lyceum, New York, November 23, 1900. Quoted in Mark Twain's Speeches (1910), ed. William Dean Howells, p. 146 http://books.google.com/books?id=7etXZ5Q17ngC&pg=PA146 (The speech is titled "Public Education Association" in that book, but also referred to elsewhere as his "I am a Boxer" speech.)
On the Decay of the Art of Lying http://www.gutenberg.org/cache/epub/2572/pg2572.html
In revised edition, chapter 78, p. 401, The Autobiography of Mark Twain, 1959, Charles Neider, Harper & Row
Mark Twain's Autobiography (1924)
"Taming the Bicycle" (1917)
“A circle is a round straight line with a hole in the middle.”
Quoting a schoolchild in "English as She Is Taught"
On the Book of Mormon, Roughing It (published 1872), pp. 58-59
Roughing It (1872)
Concerning the Jews (Harper's Magazine, Sept. 1899)
Variante: I have no race prejudices nor caste prejudices nor creed prejudices. All I care to know is that a man is a human being, and that is enough for me; he can't be any worse.
“I don't see no p'ints about that frog that's any better'n any other frog.”
"The Celebrated Jumping Frog of Calaveras County" (1865)
Letter of acceptance of membership to Concord Free Trade Club (March 28, 1885): Mark Twain, his life and work: a biographical sketch (1892), William Montgomery Clemens, Clemens Pub. Co.
Statements (c. December 1907), in Mark Twain In Eruption : Hitherto Unpublished Pages About Men And Events (1940) edited by Bernard Augustine De Voto
Quelle: Autobiography of Mark Twain, Vol. 3 (2015), p. 245
Quelle: Autobiography of Mark Twain, Vol. 3 (2015), p. 288
New England Weather, speech to the New England Society (December 22, 1876)