Mark Twain: Man

“If you pick up a starving dog and make him prosperous he will not bite you. This is the principal difference between a dog and man.”

Mark Twain

Variant: If you pick up a starving dog and make him prosperous, he will not bite you. This is the principal difference between a dog and a man.

Dogs

“A man is accepted into a church for what he believes and he is turned out for what he knows.”

Mark Twain

“Of all the creatures that were made he [man] is the most detestable. Of the entire brood he is the only one — the solitary one — that possesses malice. That is the basest of all instincts, passions, vices — the most hateful…He is the only creature that inflicts pain for sport, knowing it to be pain…Also — in all the list he is the only creature that has a nasty mind.”

Mark Twain

Vol. II, p. 7
Mark Twain's Autobiography (1924)

Pain , Hate , Sport , Passion

“The fear of death follows from the fear of life. A man who lives fully is prepared to die at any time.”

Mark Twain

Not by Twain, but from Edward Abbey's A Voice Crying In The Wilderness (1989).
Misattributed

Depressing , Heart Touching , Life , Death

“When I was a boy of 14, my father was so ignorant, I could hardly stand to have the old man around. But when I got to be 21, I was astonished at how much the old man had learned in seven years.”

Mark Twain

Not found in Twain's works, this was attributed to him in Reader's Digest (September 1939): no prior attribution known. Mark Twain’s father died when Twain was eleven years old.
Disputed
Variant: When I was a boy of fourteen, my father was so ignorant I could hardly stand to have the old man around. But when I got to be twenty-one, I was astonished at how much the old man had learned in seven years.

Father's Day , For Father , Boy , Learning

“When a man loves cats, I am his friend and comrade, without further introduction.”

Mark Twain

Source: Who Is Mark Twain?

Love , Cats

“When I was a boy a farmer's wife who lived five miles from our village had great fame as a faith-doctor—that was what she called herself. Sufferers came to her from all around, and she laid her hand upon them and said, "Have faith—it is all that is necessary," and they went away well of their ailments. She was not a religious woman, and pretended to no occult powers. She said that the patient's faith in her did the work. Several times I saw her make immediate cures of severe toothaches. My mother was the patient. In Austria there is a peasant who drives a great trade in this sort of industry, and has both the high and the low for patients. He gets into prison every now and then for practising without a diploma, but his business is as brisk as ever when he gets out, for his work is unquestionably successful and keeps his reputation high. In Bavaria there is a man who performed so many great cures that he had to retire from his profession of stage-carpentering in order to meet the demand of his constantly increasing body of customers. He goes on from year to year doing his miracles, and has become very rich. He pretends to no religious helps, no supernatural aids, but thinks there is something in his make-up which inspires the confidence of his patients, and that it is this confidence which does the work, and not some mysterious power issuing from himself.”

Mark Twain Christian Science

Source: Christian Science (1907), Ch. 4

Faith , Confidence , Boy , Business

“The Jew has his other side. He has some discreditable ways, though he has not a monopoly of them… He has a reputation for various small forms of cheating, and for practising oppressive usury, and for burning himself out to get the insurance, and for arranging cunning contracts which leave him an exit but lock the other man in, and for smart evasions which find him safe and comfortable just within the strict letter of the law, when court and jury know very well that he has violated the spirit of it.”

Mark Twain book Concerning the Jews

Concerning the Jews (Harper's Magazine, Sept. 1899)