“Kindness is the language which the deaf can hear and the blind can see.”
Unsourced in The Philosophy of Mark Twain: The Wit and Wisdom of a Literary Genius (2014) by David Graham
Disputed
“Always do what is right. It will gratify half of mankind and astound the other.”
To the Young People's Society, Greenpoint Presbyterian Church, Brooklyn (February 16, 1901).
Variant: Always do right. This will gratify some people, and astonish the rest.
“You can't depend on your eyes when your imagination is out of focus.”
Ch. 43 http://www.literature.org/authors/twain-mark/connecticut/chapter-43.html
Source: A Connecticut Yankee in King Arthur's Court (1889)
“Clothes make the man. Naked people have little or no influence on society.”
More Maxims of Mark (1927) edited by Merle Johnson
Variant: Clothes make the man. Naked people have little or no influence on society.
Source: Following the Equator (1897), Ch. LXII
Pudd'nhead Wilson's New Calendar, Ch. XV
Misquoted as "Why shouldn’t truth be stranger than fiction? Fiction, after all, has to make sense." by Laurence J. Peter in "Peter’s Quotations: Ideas for Our Time", among many others.
Following the Equator (1897)
Source: Following the Equator: A Journey Around the World
Letter to George Bainton, 15 October 1888, solicited for and printed in George Bainton, The Art of Authorship: Literary Reminiscences, Methods of Work, and Advice to Young Beginners (1890), pp. 87–88 http://books.google.com/books?id=XjBjzRN71_IC&pg=PA87.
Twain repeated the lightning bug/lightning comparison in several contexts, and credited Josh Billings for the idea:
Josh Billings defined the difference between humor and wit as that between the lightning bug and the lightning.
Speech at the 145th annual dinner of St. Andrew's Society, New York, 30 November 1901, Mark Twain Speaking (1976), ed. Paul Fatout, p. 424
Billings' original wording was characteristically affected:
Don't mistake vivacity for wit, thare iz about az mutch difference az thare iz between lightning and a lightning bug.
Josh Billings' Old Farmer's Allminax, "January 1871" http://books.google.com/books?id=sUI1AAAAMAAJ&pg=PT30. Also in Everybody's Friend, or; Josh Billing's Encyclopedia and Proverbial Philosophy of Wit and Humor (1874), p. 304 http://books.google.com/books?id=7rA8AAAAYAAJ&pg=PA304
Source: The Wit and Wisdom of Mark Twain
“I did not attend his funeral, but I sent a nice letter saying I approved of it.”
Variant: I didn’t attend the funeral, but I sent a nice letter saying that I approved of it.
“Reader, suppose you were an idiot. And suppose you were a member of Congress. But I repeat myself.”
Draft manuscript (c.1881), quoted by Albert Bigelow Paine in Mark Twain: A Biography (1912), p. 724 http://books.google.com/books?id=2UYLAAAAIAAJ&pg=PA724#v=onepage&q&f=false
Variant: Suppose you were an idiot, and suppose you were a member of Congress; but I repeat myself.
“A lie can travel half way around the world while the truth is putting on its shoes.”
Variant: A lie can travel halfway around the world while the truth is putting on its shoes.
The Mysterious Stranger (1916)
“The minority is always in the right. The majority is always in the wrong.”
Attributed to Twain, but never sourced. Suspiciously close to "A minority may be right, and the majority is always in the wrong." — Henrik Ibsen "Enemy of the People," as well as a famous quote from Danish philosopher Søren Kierkegaard
Misattributed
Mark Twain in Eruption: Hitherto Unpublished Pages About Men and Events (1940) edited by Bernard DeVoto
This quote has been attributed to Mark Twain, but the attribution cannot be verified. The quote should not be regarded as authentic. — Twainquotes http://www.twainquotes.com/Discovery.html
Actually from the 1990 book P. S. I Love You' https://books.google.com/books?id=5OORXU6rlGIC&q=bowlines#v=onepage&q=bowlines&f=false' by H. Jackson Brown.
Misattributed