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Sir Isaac Newton (25 Dec 1642 - 20 Mar 1727) English physicist and mathematician who made seminal discoveries in several areas of science, and was the leading scientist of his era. Short biography of Sir Isaac Newton >>

Isaac Newton
“The cause of gravity is what I do not pretend to know”

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by Frits Ahlefeldt (source)

“You sometimes speak of gravity as essential and inherent to matter. Pray do not ascribe that notion to me, for the cause of gravity is what I do not pretend to know, and therefore would take more time to consider of it.”

— Isaac Newton

From Letter to Richard Bentley (1693).

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This quote is from Newton’s correspondence with theologian Richard Bentley, who in 1692 delivered a series of sermons on the subject of “A Confutation of Atheism from the Origin and Frame of the World” at St. Martin-in-the-Field. This course of lectures was the first on the evidence of Christianity established by a bequest from Robert Boyle.

In preparing his sermons, Bentley had received Newton’s recommendations, in July 1691, for background information from parts of the Principia which had been published about five years earlier. After Bentley gave his oral presentations, but before publishing them, he consulted with Isaac Newton in several letters, clarifying a number of points regarding gravity and cosmogony, so that he could be sure the printed version of his lectures gave a correct interpretation of Newton’s ideas.

In Newton’s first reply (10 Dec 1692), he made his deep religious belief clear in his opening:

“When I wrote my treatise about our Systeme I had an eye upon such Principles as might work with considering men for the beleife of a Deity & nothing can rejoyce me more then to find it usefull for that purpose But if I have done the publick any service this way 'tis due to nothing but industry & a patient thought.”

Later in that same letter, Newton referred to the planets and their moons (the secondary planets):

“To your second Query I answer that the motions which the Planets now have could not spring from any naturall cause alone but were imprest by an intelligent Agent … its plaine that there is no naturall cause which could determin all the Planets both primary & secondary to move the same way & in the same plane without any considerable variation. This must have been the effect of Counsel.”

Bentley may have sent copies of the oral lectures to Newton (of which only one letter from Bentley survives). In one of these lost letters, it seems Newton felt his own views on gravity were somewhat misrepresented, so at the end of his second letter (17 January 1692/3) to Bentley about the lectures, Newton makes clear that he denies knowing gravity's cause:

“You sometimes speak of gravity as essential & inherent to matter: pray do not ascribe that notion to me, for ye cause of gravity is what I do not pretend to know, & therefore would take more time to consider of it.”

Within his fourth reply to Bentley, Newton included more on his view of gravity, in which he uses the word “immaterial” in the sense of being spiritual, rather than physical (material):

“Gravity must be caused by an agent [acting] consta[ntl]y according to certain laws, but whether this agent be material or immaterial is a question I have left to the consideration of my readers.”

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