I decided to track down the quotes I was thinking of in making my assertions. I found that I've made a mistake in saying Newton is the counter-example to Humean causation. What I was thinking was Newton, but that's not really stated in the quotes I was thinking of.
Something very much like the argument I outlined is there -- but not Newton. So, my bad there. But, to go over the quotes I was thinking. . .
In the preface to the 2nd edition, at the end of B
x:
Two [sciences involving] theoretical cognitions by reason are to determine their objects a priori: they are mathematics and physics. In mathematics this determination is to be entirely pure; in physics it is to be at least partly pure, but to some extent also in accordance with sources of cognition other than reason
That's definitely the quote I was thinking of in saying Newton, though this in particular doesn't link physics to Newton (as K. was definitely interested in physics at large, and not just Newton), or how that might serve as a counter-example to Humean criticisms of causation.
Later, on B21 there is a footnote in the introduction to the second edition, 2 paragraphs after introducing the central question of the critique, to these lines:
How is pure mathematics possible?
How is pure natural science possible?
Since these sciences are actually given [as existent], it is surely proper for us to ask how they are possible; for that they must be possible is proved by their being actual.
And the footnote reads:
This actuality may still be doubted by some in the case of pure natural science. Yet we need only examine the propositions that are to be found at the beginning of physics proper (empirical physics), such as those about the permanence of the quantity of matter, about inertia, about the equality of action and reaction, etc., in order to soon be convinced that these propositions themselves amount to a physica pura (or physica rationalis). Such a physics, as a science in its own right, surely deserves to be put forth separately and in its whole range, whether this range be narrow or broad
To this footnote the translator adds a footnote of his own, appended to the last sentence:
This Kant did in his Metaphysical Foundations of Natural Science (1786), Ak. IV, 465-565
This is where I got the notion of him deriving Newtonian physics, but surely Newton is not mentioned here either. Nor is the notion of Newtonian physics serving as
the counter-example against Humean skepticism.
Earlier in the introduction, under II. "We are in Possession of Certain A Priori Cognitions, And Even Common Understanding is Never without Them" at B5 Kant stated:
...Now, it is easy to show that in human cognition there actually are such judgments, judgments that are necessary and in the strictest sense universal, and hence are pure a priori judgments. If we want an example from the sciences, we need only look to all the propositions of mathematics; if we want one from the most ordinary use of understanding, then we can use the proposition that all change must have a cause.
This is getting closer to how Kant is in disagreement with Hume, and highlighting a sort of principle which the common understanding uses (though, perhaps, this principle isn't something that Newton uses -- again, no support for that particular claim of mine).
Later we get closer to the language I used, albeit admittedly not with Newton referenced. I'll just note here I'm now uncertain why I thought Newton in particular to Hume. Kant certainly references Newtonian physics throughout the CPR, but I overstepped in stating that it was Newton who served as the counter to Humean skepticism, I believe, unless there's some reference I missed. However, even in that case I overstepped, because after reading this highlighted portion I'm pretty sure this is where I was getting everything I stated before. So even if the reference is there, I was in error because these were the sections I was thinking of anyways.
Mea culpa.
At B127, or in the section titled "Transition to the Transcendental Deduction of the Categories":
The illustrious Locke, not having engaged in this contemplation, and encountering pure concepts of understanding in experience, also derived them from experience. Yet he proceeded so inconsistently that he dared to try using these concepts for cognitions that go far beyond any boundary of experience. David Hume recognized that in order for us to be able to do this, the origin of these concepts must be a priori. But he was quite unable to explain how it is possible that concepts not in themselves combined in the understanding should nonetheless have to be thought by it as necessarily combined in the object. Nor did it occur to him that perhaps the understanding itself might, through these concepts, be the author of the experience wherein we encounter the understanding's objects. Thus, in his plight, he derived these concepts from experience (viz. from habit, a subjective necessity that arises in experience through repeated association and that ultimately is falsely regarded as objective). But he proceeded quite consistently after that, for he declared that we cannot use these concepts and the principles that they occasion in order to go beyond the boundary of experience. Yet the empirical derivation of these concepts which occurred to both cannot be reconciled with the scientific a priori cognitions that we actually have, viz., our a priori cognitions of pure mathematics and universal natural science, and hence this empirical derivation is refuted by that fact.
That last sentence, in particular, is pretty much what I was thinking of. I believe I must have basically interpreted "universal natural science" as equivalent to Newtonian physics, though by no means is that asserted here.
The facts, though, which are meant to stand as counter-examples to the Humean account of causation are the sciences of pure mathematics, and universal natural science.