Natural Selection Seems Insufficient

[Jal]

This is Newton saying, "If you believe in an immaterial force acting across a distance, you must be an idiot."

I think we can make this clearer if we quote more of the letter:

Here is the paragraph:

Tis unconceivable that inanimate brute matter should (without the mediation of something else which is not material) operate upon & affect other matter without mutual contact; as it must if gravitation in the sense of Epicurus be essential & inherent in it. And this is one reason why I desired you would not ascribe {innate} gravity to me. That gravity should be innate inherent & {essential} to matter so that one body may act upon another at a distance through a vacuum without the mediation of any thing else by & through which their action or force {may} be conveyed from one to another is to me so great an absurdity that I beleive no man who has in philosophical matters any competent faculty of thinking can ever fall into it. Gravity must be caused by an agent {acting} <7v> 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.

It's clear that he's arguing against the theory of Epicurus, who said that gravity is an inherent quality of objects. 

Instead, he is proposing that gravity must be caused by an agent which acts according to certain laws, and that this agent may be immaterial. It is not something essential to or contained within the heavy object -- it is a force which acts on the heavy object. 

So he's defending his view that gravity is an agent (we would be more likely to say "force"), which exists, which is immaterial, and which acts on objects through a vacuum.

The first part of the first sentence says that physical objects at a distance cannot affect each other unless there is some immaterial agent mediating. The immaterial agent is gravity.

It's true that Newton never says exactly what gravity is, other than to say, basically, it's a force which does the things that gravity does. He doesn't feel he has to say what it is or where it came from, he only has to describe how it acts. 

This is all part of a larger project to dismantle Aristotle's mechanics. Aristotle said that things can only move because they are influenced by physical interactions -- i.e., they get pushed by some material object. Aristotle's theories of motion and mechanics had been seen as outdated since the 14th century, when a group of theologians known as the Oxford Calculators used a combination of empirical experiment and math to show that his ideas about acceleration were incorrect. Still, Newton and Bentley were careful to show in exactly what way they disagreed with Aristotle and Epicurus.

Here is the full letter:

https://www.newtonproject.ox.ac.uk/view/...20of%20any

Any allowance of immateriality is idiocy in my view, especially when it is alleged to push or pull material objects.  

But fair enough. Newton evidently allowed the possibility of immaterial realities. This is not really a surprise, since he held to at least some of the traditional Christian beliefs, which generally involve an immaterial realm. He vacillated over whether gravity was the hand of God - and I suppose for him, it would mean an immaterial hand/God. 

Setting aside God for the moment,  he did commit to a medium of some kind.