“Thanne is it wysdom, as it thynketh me,
To maken vertu of necessity,”

Quote in Vincent's letter to Theo van Gogh, from The Hague, 3 June 1883; as cited in Stranger on the Earth : A Psychological Biography of Vincent Van Gogh (1996) by Albert J. Lubin, p. 22
Variant translation: For me, the work is an absolute necessity. I cannot put it off; I don't care for anything else; that is to say, the pleasure in something else ceases at once, and I become melancholy when I cannot go on with my work. I feel then as the weaver does when he sees that his threads have got tangled, the pattern he had on the loom has gone to the deuce, and his exertion and deliberation are lost.
As quoted in Dear Theo: the Autobiography of Vincent Van Gogh (1995) edited by Irving Stone and Jean Stone, p. 204
1880s, 1883
Context: The work is an absolute necessity for me. I can't put it off, I don't care for anything but the work; that is to say, the pleasure in something else ceases at once and I become melancholy when I can't go on with my work. Then I feel like a weaver who sees that his threads are tangled, and the pattern he had on the loom is gone to hell, and all his thought and exertion is lost.

As quoted in The Man from Monticello : An Intimate Life of Thomas Jefferson (1969) by Thomas J. Fleming, p. 250
Posthumous publications

Letter 10, 3.
Letters, Book IV

"Rome, 9 January"
Without Dogma (1891)
Context: My position is such that there is no necessity for me to enter into competition with struggling humanity. As to expensive and ruinous pleasures, I am a sceptic who knows how much they are worth, or rather, knows that they are not worth anything.

Authors Take Sides on the Spanish War (1937) edited by Nancy Cunard and published by the Left Review
Context: As for 'taking sides' — the choice, it seems to me, is no longer between two users of violence, two systems of dictatorship. Violence and dictatorship cannot produce peace and liberty; they can only produce the results of violence and dictatorship, results with which history has made us only too sickeningly familiar. The choice now is between militarism and pacifism. To me, the necessity of pacifism seems absolutely clear.

Source: Diaries of Franz Kafka

Source: Attributed in posthumous publications, Einstein and the Poet (1983), p. 89
Context: The God Spinoza revered is my God, too: I meet Him everyday in the harmonious laws which govern the universe. My religion is cosmic, and my God is too universal to concern himself with the intentions of every human being. I do not accept a religion of fear; My God will not hold me responsible for the actions that necessity imposes. My God speaks to me through laws.

Lib. 8, Ep. 11, sect. 4; vol. 2, p. 463.
Epistularum