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Re: [Phys-l] Newton and causation



I'm not terribly interested in worrying about what Newton might have thought about causation within the context of the second law, but from my perusing (and "perusing" it certainly is) of the Principia, I doubt that there is much evidence for him holding any particular position. If anything, it seems to me that he might hold that it can go either way if only because of his, to be blunt, strikingly muddled and inconsistent language in this area. For instance, in his "Definitions" he distinguishes between "the inherent force of matter" (which is exerted BY a body only when it changes its state of motion because of the change in motion), "impressed force" (which is exerted ON a body in order to change its state of motion), and "centripetal force" (which comes in three varieties: absolute, accelerative, and motive.)

In any event, I don't think that Newton's well-known and laudable position with regard to the "causes" of gravity bears on his general sympathy for the existence of causes in general. He wrote that in natural philosophy we must "begin from phenomena and admit no principles of things, no causes, no explanations, except those which are established through phenomena." Note that he does not suggest that there are no causes nor even that they may not be established through experiment.

John Mallinckrodt
Cal Poly Pomona

On Jan 11, 2011, at 12:16 PM, John Denker wrote:

On 01/11/2011 12:47 PM, ludwik kowalski wrote:

change in momentum = impulse

does not address the issue "what causes what."

Agreed!

But I suspect that
Newton did address the issue. He probably wrote that change in
momentum results from an impulse.

Absolutely not.

Newton, like Galileo before him, emphatically explained that the
laws of motion do not say anything about causation.

Can someone to either confirm or
refute this?

I quote from http://www.isaacnewton.ca/gen_scholium/scholium.htm

But hitherto I have not been able to discover the cause of those
properties of gravity from phænomena, and I frame no hypotheses.....
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.

I do not have an easy access to his Principia.

It's online in dozens of places.

http://www.google.com/search?q=%22hypotheses+non+fingo%22
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