Public statements on Mechanism by Newton

The object of the mechanical philosophy was precisely to exclude from accounts of Nature all terms that were not strictly definable and complete in themselves; such term as time, space, mass, shape and motion only were to figure in scientific discussion at the fundamental level.

Below are some of Newton's public statements made after the publication of Principia. His rich sequence of private hypotheses, begun as an undergraduate, are not dealt with here.

Tis unconceivable that inanimate brute matter should (without the mediation of something else which is not material) operate upon and affect other matter without mutual contact; as it must if gravitation in the sense of Epicurus be essential and 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 and 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 and 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 constantly according to certain laws, but whether this agent be material or immaterial is a question I have left to the consideration of my readers.

Newton to Bentley, 25 February 1692/3 (Bentley was collecting material for the Boyle Lecture he was about to deliver.)

For it's well known, that Bodies act one upon another by the Attractions of Gravity, Magnetism, and Electricity; and these Instances shew the Tenor and Course of Nature, and make it not improbable but that there may be more attractive Powers than these. For Nature is very consonant and conformable to her self. How these Attractions may be perform'd, I do not here consider. What I call Attraction may be perform'd by impulse, or by some other means unknown to me. I use that Word to signify only in general any Force by which Bodies tend towards one another, whatsoever be the Cause. For we must learn from the Phænomena of Nature what Bodies attract one another, and what are the Laws and Properties of the Attraction, before we enquire the Cause by which the Attraction is perform'd.

From Newton's English version of Opticks Query 31, although this query first appeared in the Latin edition of 1706 (Opticks p376.)

But hitherto I have not been able to discover the cause of those properties of gravity from phenomena, and I frame no hypotheses; for whatever is not deduced from the phenomena is to be called an hypothesis; and hypotheses, whether metaphysical or physical, whether of occult qualities or mechanical, have no place in experimental philosophy. In this philosophy particular propositions are inferred from the phenomena, and afterwards rendered general by induction. Thus it was that the impenetrability, the mobility, and the impulsive force of bodies, and the laws of motion and of gravitation, were discovered. And to us it is enough that gravity does really exist, and act according to the laws which we have explained, and abundantly serves to account for all the motions of the celestial bodies, and of our sea.

From the General Scholium, printed in 1713 (Principia p546.) The phrase I frame no hypotheses (hypotheses non fingo in Newton's Latin) is from Motte's translation of 1729, when frame carried a pejorative sense as fingo could. feign has been suggested as a suitable modern translation. I would suggest I am fabricating which is one of the usual meanings of fingo in both literal and figurative senses, and can sound suitably pejorative to modern readers.

The Philosophy which Mr. Newton in his Principles and Optiques has pursued is Experimental; and it is not the Business of Experimental Philosophy to teach the Causes of things any further than they can be proved by Experiments. We are not to fill this Philosophy with Opinions which cannot be proved by Phænomena. In this Philosophy Hypotheses have no place, unless as Conjectures or Questions proposed to be examined by Experiments. For this Reason Mr. Newton in his Optiques distinguished those things which were made certain by Experiments from those things which remained uncertain, and which he therefore proposed in the End of his Optiques in the Form of Queries.

From An Account of the Book entituled Commercium Epistolicum, published anonymously by Newton in the Philosophical Transactions 29 (1714-15): 222-224. This passage provides a bridge between the seemingly positivist General Scholium above and the speculative Query 21 below.

Is not this Medium much rarer within the dense Bodies of the Sun, Stars, Planets and Comets, than in the empty celestial Spaces between them? And in passing from them to great distances, doth it not grow denser and denser perpetually, and thereby cause the gravity of those great Bodies towards one another, and of their parts towards the Bodies; every Body endeavouring to go from the denser parts of the Medium towards the rarer?

A discussion of the Æther from Opticks Query 21, which appeared in 1717 (Opticks p350.)