“I could give here several other ways of tracing and conceiving a series of curved lines, each curve more complex than any preceding one, but I think the best way to group together all such curves and them classify them in order, is by recognizing the fact that all points of those curves which we may call "geometric," that is, those which admit of precise and exact measurement, must bear a definite relation to all points of a straight line, and that this relation must be expressed by a single equation. If this equation contains no term of higher degree than the rectangle of two unknown quantities, or the square of one, the curve belongs to the first and simplest class, which contains only the circle, the parabola, the hyperbola, and the ellipse; but when the equation contains one or more terms of the third or fourth degree in one or both of the two unknown quantities (for it requires two unknown quantities to express the relation between two points) the curve belongs to the second class; and if the equation contains a term of the fifth or sixth degree in either or both of the unknown quantities the curve belongs to the third class, and so on indefinitely.”
Second Book
La Géométrie (1637)
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René Descartes 47
French philosopher, mathematician, and scientist 1596–1650Related quotes

"Boscovich's mathematics", an article by J. F. Scott, in the book Roger Joseph Boscovich (1961) edited by Lancelot Law Whyte.
"Transient pressure analysis in composite reservoirs" (1982) by Raymond W. K. Tang and William E. Brigham.
"Non-Newtonian Calculus" (1972) by Michael Grossman and Robert Katz.

“Our course of advance … is neither a straight line nor a curve. It is a series of dots and dashes.”
Other writings, The Paradoxes of Legal Science (1928)
Context: Our course of advance... is neither a straight line nor a curve. It is a series of dots and dashes. Progress comes per saltum, by successive compromises between extremes, compromises often … between "positivism and idealism". The notion that a jurist can dispense with any consideration as to what the law ought to be arises from the fiction that the law is a complete and closed system, and that judges and jurists are mere automata to record its will or phonographs to pronounce its provisions.

“The straight line belongs to Man. The curved line belongs to God.”
The real author seems to be Pierre Albert-Birot https://books.google.com/books?id=3Ul51CwjUOcC&pg=PA290&dq=%22the+curved+line+that+belongs+let%27s+say+to+God+and+the+straight+line+that+belongs+to+man%22&hl=de&sa=X&redir_esc=y#v=onepage&q=%22the%20curved%20line%20that%20belongs%20let%27s%20say%20to%20God%20and%20the%20straight%20line%20that%20belongs%20to%20man%22&f=false.
Attributed

“A Curve does not exist in its full power until contrasted with a straight line.”