“To challenge and to cope with this paradoxical state of things, we need a paradoxical way of thinking; since the world drifts into delirium, we must adopt a delirious point of view. We must no longer assume any principle of truth, of causality, or any discursive norm. Instead, we must grant both the poetic singularity of events and the radical uncertainty of events. It is not easy. We usually think that holding to the protocols of experimentation and verification is the most difficult thing. But in fact the most difficult thing is to renounce the truth and the possibility of verification, to remain as long as possible on the enigmatic, ambivalent, and reversible side of thought.”

'La vie n’est facile pour aucun de nous. Mais quoi, il faut avoir de la persévérance, et surtout de la confiance en soi. Il faut croire que l’on est doué pour quelque chose, et que, cette chose, il faut l'atteindre coûte que coûte.'
As quoted in Madame Curie : A Biography (1937) by Eve Curie Labouisse, Part 2, p. 116

Willie's Question
The Disciple and Other Poems (1867)

On Euler's identity, <math>e^{i \pi} + 1 = 0. \,\!</math> as quoted in notes by W. E. Byerly, published in Benjamin Peirce, 1809-1880 : Biographical Sketch and Bibliography (1925) by R. C. Archibald; also in Mathematics and the Imagination (1940) by Edward Kasner and James Newman.

The Philosophy of Space and Time (1928, tr. 1957)

Reported in Josiah Hotchkiss Gilbert, Dictionary of Burning Words of Brilliant Writers (1895), p. 6

As quoted by Max Jammer, Concepts of Simultaneity: From Antiquity to Einstein and Beyond (2008)
Context: Our conscious appreciation of the fact that one event follows another is of a different kind from our awareness of either event separately. If two events are to be represented as occurring in succession, then—paradoxically—they must also be thought of simultaneously.

Source: Three Men in a Boat

Source: Synchronicity: An Acausal Connecting Principle (1960), p. 5
Context: We Shall Naturally look round in vain the macrophysical world for acausal events, for the simple reason that we cannot imagine events that are connected non-causally and are capable of a non-causal explanation. But that does not mean that such events do not exist... The so-called "scientific view of the world" based on this can hardly be anything more than a psychologically biased partial view which misses out all those by no means unimportant aspects that cannot be grasped statistically.