“No variation of things arises from blind metaphysical necessity, which must be the same always and everywhere.” [A cæca necessitate metaphysica, quæ utique eadem est semper & ubique, nulla oritur rerum variatio.]--Isaac Newton, General Scholium (1713), Principia.
This week we're celebrating three hundred years since Newton published the General Scholium, attached to the second edition of the Principia. The passage above was only inserted in the final (1726), third edition. The argument of the sentence seems to be something like this:
- A1: (Metaphysical) Necessity <--> Homogeneity
- A2: Homogeneity and Variety are disjunctive alternatives (suppressed premise)
- P: We observe variety
- Therefore, no metaphysical necessity
Even so, given the text of Spinoza's Ethics, it is puzzling that Newton treats the Spinozistic argument as being committed to the idea that metaphysical necessity implies homogeneity. Now, as Newton's earliest critics realized (here's Jonathan Edwards) the argument of the General Scholium is very indebted to Clarke's (1705) A Demonstration of the Being and Attributes of God (first given as a so-called Boyle lectures in 1704). Clarke's Demonstration is as the sub-title helpfully explains offered "in answer to Mr. Hobbes, Spinoza, and their followers." Clarke's arguments against Spinoza probably attracted the attention of Hume, and have had a surprising afterlife in the origin of analytical philosophy.
The argument is likewise the same in the question about the origin of motion. Motion cannot be necessarily existing because, it being evident that all determinations are equally possible in themselves, the original determination of the motion of any particular body this way rather than the contrary way could not be necessary in itself, but was either caused by the will of an intelligent and free agent, or else was an effect produced and determined without any cause at all, which is an express contradiction: as I have shown in my Demonstration. (Clarke to Butler, Dec 10, 1713)