“Whatever is well conceived is clearly said,
And the words to say it flow with ease.”
Ce que l'on conçoit bien s'énonce clairement,
Et les mots pour le dire arrivent aisément.
Canto I, l. 153
The Art of Poetry (1674)
Original
Ce que l'on conçoit bien, s'énonce clairement, Et les mots pour le dire arrivent aisément.
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Nicolas Boileau-Despréaux 30
French poet and critic 1636–1711Related quotes

“Whatever you might say the object "is", well it is not.”
Source: Science and Sanity (1933), p. 35.
Context: "Say whatever you choose about the object, and whatever you might say is not it." Or, in other wordsː "Whatever you might say the object "is", well it is not." This negative statement is final, because it is negative.

“Whatever is worth saying, can be stated in fifty words or less.”
as quoted by Gian-Carlo Rota in Words spoken at the memorial service for S. M. Ulam (The Lodge, Los Alamos, New Mexico, May 17, 1984), published in The Mathematical Intelligencer, Volume 6, Number 4 / December, 1984

27
Les Caractères (1688), De la société et de la conversation
Context: To speak and to offend is with some people but one and the same thing; they are biting and bitter; their words are steeped in gall and wormwood; sneers as well as insolent and insulting words flow from their lips. It had been well for them had they been born mute or stupid; the little vivacity and intelligence they have prejudices them more than dullness does others; they are not always satisfied with giving sharp answers, they often attack arrogantly those who are present, and damage the reputation of those who are absent; they butt all round like rams — for rams, of course, must use their horns. We therefore do not expect, by our sketch of them, to change such coarse, restless, and stubborn individuals. The best thing a man can do is to take to his heels as soon as he perceives them, without even turning round to look behind him.

Adagio (2004)
Examples of self-translation (c. 2004)

On an interview on The O'Reilly Factor (6 February 2016)
2010s, 2016, February

“Let no one persuade you by word or deed to do or say whatever is not best for you.”
As quoted in Divine Harmony: The Life and Teachings of Pythagoras by John Strohmeier and Peter Westbrook. (1999)
The Golden Verses
Context: Many words befall men, mean and noble alike; do not be astonished by them, nor allow yourself to be constrained.
If a lie is told, bear with it gently.
But whatever I tell you, let it be done completely.
Let no one persuade you by word or deed to do or say whatever is not best for you.

A Persian Song of Hafiz, reported in Bartlett's Familiar Quotations, 10th ed. (1919). Compare: "'T was he that ranged the words at random flung, Pierced the fair pearls and them together strung", Eastwick: Anvari Suhaili. (Translated from Firdousi).