“The sentiment of reality can indeed attach itself so strongly to our object of belief that our whole life is polarized through and through, so to speak, by its sense of the existence of the thing believed in, and yet that thing, for the purpose of definite description, can hardly be said to be present to our mind at all.”

Source: The Limits of Evolution, and Other Essays, Illustrating the Metaphysical Theory of Personal Ideaalism (1905), Later German Philosophy, p.170

Toronto, Ontario, Canada May 27, 1994
1990s

Variant transcription from "Death of a Genius" in Life Magazine: "Certainly there are things worth believing. I believe in the brotherhood of man and the uniqueness of the individual. But if you ask me to prove what I believe, I can't. You know them to be true but you could spend a whole lifetime without being able to prove them. The mind can proceed only so far upon what it knows and can prove. There comes a point where the mind takes a leap—call it intuition or what you will—and comes out upon a higher plane of knowledge, but can never prove how it got there. All great discoveries have involved such a leap."
Unsourced variant: "The intellect has little to do on the road to discovery. There comes a leap in consciousness, call it intuition or what you will, and the solution comes to you and you do not know how or why. All great discoveries are made in this way." The earliest published version of this variant appears to be The Human Side of Scientists by Ralph Edward Oesper (1975), p. 58 http://books.google.com/books?id=-J0cAQAAIAAJ&q=%22solution+comes+to+you+and+you+do+not+know%22&dq=%22solution+comes+to+you+and+you+do+not+know%22&hl=en, but no source is provided, and the similarity to the "Life Magazine" quote above suggests it's likely a misquote.
Source: Attributed in posthumous publications, Einstein and the Poet (1983), p. 136

Life Without Principle (1863)
Context: It is so hard to forget what it is worse than useless to remember! If I am to be a thoroughfare, I prefer that it be of the mountain-brooks, the Parnassian streams, and not the town-sewers. There is inspiration, that gossip which comes to the ear of the attentive mind from the courts of heaven. There is the profane and stale revelation of the bar-room and the police court. The same ear is fitted to receive both communications. Only the character of the hearer determines to which it shall be open, and to which closed. I believe that the mind can be permanently profaned by the habit of attending to trivial things, so that all our thoughts shall be tinged with triviality.

Source: The End of the Affair

Article "The Worst Man in the World" in The Sunday Dispatch (2 July 1933); quoted in The Magical Revival (1972) by Kenneth Grant.
Context: Black magic is not a myth. It is a totally unscientific and emotional form of magic, but it does get results — of an extremely temporary nature. The recoil upon those who practice it is terrific.
It is like looking for an escape of gas with a lighted candle. As far as the search goes, there is little fear of failure!
To practice black magic you have to violate every principle of science, decency, and intelligence. You must be obsessed with an insane idea of the importance of the petty object of your wretched and selfish desires.
I have been accused of being a "black magician." No more foolish statement was ever made about me. I despise the thing to such an extent that I can hardly believe in the existence of people so debased and idiotic as to practice it.

Source: 1890s, The Principles of Psychology (1890), Ch. 21

Source: Henry V

Advertisement, N.Y. Herald Tribune (August 19, 1946)