“To doubt everything or to believe everything are two equally convenient solutions; both dispense with the necessity of reflection.”
Douter de tout ou tout croire, ce sont deux solutions également commodes, qui l'une et l'autre nous dispensent de réfléchir.
Preface, Dover abridged edition (1952), p. xxii
Science and Hypothesis (1901)
Original
Douter de tout ou tout croire, ce sont deux solutions également commodes, qui l'une et l'autre nous dispensent de réfléchir.
, 1902
Help us to complete the source, original and additional information
Henri Poincaré 49
French mathematician, physicist, engineer, and philosopher … 1854–1912Related quotes
“In the arithmetic of love, one plus one equals everything, and two minus one equals nothing.”
The Complete Neurotic's Notebook (1981), Love

“Everything is false, everything is possible, everything is doubtful.”
Source: Complete Works

2012
Source: The Wheel of Time: Shamans of Ancient Mexico, Their Thoughts About Life, Death and the Universe], (1998), Quotations from A Separate Reality (Chapter 6)

“Thought is so cunning, so clever, that it distorts everything for its own convenience.”

Source: The Rebel (1951), pp. 8 - 10 as quoted in Albert Camus and the Philosophy of the Absurd';(2002) by Avi Sagi, p. 44
Context: The absurd … is an experience to be lived through, a point of departure, the equivalent, in existence of Descartes' methodical doubt. Absurdism, like methodical doubt, has wiped the slate clean. It leaves us in a blind alley. But, like methodical doubt, it can, by returning upon itself, open up a new field of investigation, and in the process of reasoning then pursues the same course. I proclaim that I believe in nothing and that everything is absurd, but I cannot doubt the validity of my proclamation and I must at least believe in my protest. The first and only evidence that is supplied me, within the terms of the absurdist experience, is rebellion … Rebellion is born of the spectacle of irrationality, confronted with an unjust and incomprehensible condition.

“To doubt God is to doubt one's own conscience, and in consequence it would be to doubt everything.”
Letter to Fr. Pastells (4 April 1893)

“My principal sin is doubt. I doubt everything, and am in doubt most of the time.”
Source: Anna Karenina Notes