“Rules for Definitions. I. Not to undertake to define any of the things so well known of themselves that the clearer terms cannot be had to explain them. II. Not to leave any terms that are at all obscure or ambiguous without definition. III. Not to employ in the definition of terms any words but such as are perfectly known or already explained.”

—  Blaise Pascal

The Art of Persuasion

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French mathematician, physicist, inventor, writer, and Chri… 1623–1662

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Blaise Pascal photo

“Rules necessary for definitions. Not to leave any terms at all obscure or ambiguous without definition; Not to employ in definitions any but terms perfectly known or already explained.”

Blaise Pascal (1623–1662) French mathematician, physicist, inventor, writer, and Christian philosopher

The Art of Persuasion

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“Rules for Demonstrations. I. Not to undertake to demonstrate any thing that is so evident of itself that nothing can be given that is clearer to prove it. II. To prove all propositions at all obscure, and to employ in their proof only very evident maxims or propositions already admitted or demonstrated. III. To always mentally substitute definitions in the place of things defined, in order not to be misled by the ambiguity of terms which have been restricted by definitions.”

Blaise Pascal (1623–1662) French mathematician, physicist, inventor, writer, and Christian philosopher

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Blaise Pascal photo

“Rules necessary for demonstrations. To prove all propositions, and to employ nothing for their proof but axioms fully evident of themselves, or propositions already demonstrated or admitted; Never to take advantage of the ambiguity of terms by failing mentally to substitute definitions that restrict or explain them.”

Blaise Pascal (1623–1662) French mathematician, physicist, inventor, writer, and Christian philosopher

The Art of Persuasion

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“Most controversies would soon be ended, if those engaged in them would first accurately define their terms, and then adhere to their definitions.”

Tryon Edwards (1809–1894) American theologian

Source: A Dictionary of Thoughts, 1891, p. 88.

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“A definition, if it is to be called perfect, must explain the inmost essence of a thing, and must take care not to substitute for this any of its properties.”

Baruch Spinoza (1632–1677) Dutch philosopher

XII, 95
On the Improvement of the Understanding (1662)
Context: A definition, if it is to be called perfect, must explain the inmost essence of a thing, and must take care not to substitute for this any of its properties. In order to illustrate my meaning, without taking an example which would seem to show a desire to expose other people's errors, I will choose the case of something abstract, the definition of which is of little moment. Such is a circle. If a circle be defined as a figure, such that all straight lines drawn from the center to the circumference are equal, every one can see that such a definition does not in the least explain the essence of a circle, but solely one of its properties. Though, as I have said, this is of no importance in the case of figures and other abstractions, it is of great importance in the case of physical beings and realities, for the properties of things are not understood so long as their essences are unknown. If the latter be passed over, there is necessarily a perversion of the succession of ideas which should reflect the succession of nature, and we go far astray from our object.

Richard Whately photo

“Of Rhetoric various definitions have been given by different writers; who, however, seem not so much to have disagreed in their conceptions of the nature of the same thing, as to have had different things in view while they employed the same term.”

Richard Whately (1787–1863) English rhetorician, logician, economist, and theologian

Introduction, p. 1
Elements of Rhetoric (1828)

Blaise Pascal photo

“Rules for Axioms. I. Not to omit any necessary principle without asking whether it is admittied, however clear and evident it may be. II. Not to demand, in axioms, any but things that are perfectly evident in themselves.”

Blaise Pascal (1623–1662) French mathematician, physicist, inventor, writer, and Christian philosopher

The Art of Persuasion

William H. McNeill photo

“When terms… evolve and change definition with time; and when the social reality which terms are intended to organize and render intelligible is also seen to be in flux, capturing the truth in a net of words becomes a matter of intuition and style more than of any scientific method that can be replicated by others and made to achieve the same result every time someone asks the same question, or undertakes the same operations.”

William H. McNeill (1917–2016) Canadian historian

Discrepancies among the Social Sciences (1981)

“Physics seems to have done reasonably well in studying electrons, although there is not to this day a precise definition of this term.”

Stephen Kosslyn (1948) American psychologist

Source: Image and Mind. 1980, p. 470

Benjamin Ricketson Tucker photo

“Anarchists, whose mission in the world is the abolition of aggression and all the evils that result therefrom, perceived that, to be understood, they must attach some definite and avowed significance to the terms which they are obliged to employ, and especially to the words "State" and "government."”

Benjamin Ricketson Tucker (1854–1939) American journalist and anarchist

The Relation of the State to the Invididual (1890)
Context: Anarchists, whose mission in the world is the abolition of aggression and all the evils that result therefrom, perceived that, to be understood, they must attach some definite and avowed significance to the terms which they are obliged to employ, and especially to the words "State" and "government." Seeking, then, the elements common to all the institutions to which the name "State" has been applied, they have found them two in number: first, aggression; second, the assumption of sole authority over a given area and all within it, exercised generally for the double purpose of more complete oppression of its subjects and extension of its boundaries.

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