“I am interested in madness. I believe it is the biggest thing in the human race, and the most constant.”

As quoted in The New York Post (1 May 1959)

Source: Castle Series, Castle in the Air (1990), p. 31.
Context: "Maybe," he said, "you should be more careful about whom you let your dog bite."
"Not I!" said Jamal. "I am a believer of free will. If my dog chooses to hate the whole human race except myself, it must be free to do so."

Vit. Anon, page 64 (Plumptre's Trans.).
Bartlett's Familiar Quotations, 10th ed. (1919)

“With Your Whole Heart Jumping”

Source: Autobiography of Mark Twain, Vol. 3 (2015), p. 130
Context: I have not read Nietzsche or Ibsen, nor any other philosopher, and have not needed to do it, and have not desired to do it; I have gone to the fountain-head for information—that is to say, to the human race. Every man is in his own person the whole human race, with not a detail lacking. I am the whole human race without a detail lacking; I have studied the human race with diligence and strong interest all these years in my own person; in myself I find in big or little proportion every quality and every defect that is findable in the mass of the race. I knew I should not find in any philosophy a single thought which had not passed through my own head, nor a single thought which had not passed the heads of millions and millions of men before I was born; I knew I should not find a single original thought in any philosophy, and I knew I could not furnish one to the world myself, if I had five centuries to invent it in. Nietzsche published his book, and was at once pronounced crazy by the world—by a world which included tens of thousands of bright, sane men who believed exactly as Nietzsche believed, but concealed the fact, and scoffed at Nietzsche. What a coward every man is! and how surely he will find it out if he will just let other people alone and sit down and examine himself. The human race is a race of cowards; and I am not only marching in that procession but carrying a banner.

The World Is My Home (1991)
Context: I am a humanist because I think humanity can, with constant moral guidance, create reasonably decent societies. I think that young people who want to understand the world can profit from the works of Plato and Socrates, the behaviour of the three Thomases, Aquinas, More and Jefferson — the austere analyses of Immanuel Kant and the political leadership of Abraham Lincoln and Franklin Roosevelt.

Academy of Achievement interview (1991)

Source: The Life Of My Choice (1987), p.115.

Source: The Book Thief