The work is entitled Metaphysical Foundations of Natural Science, and elsewhere, as in the Groundwork of the Metaphysics of Morals, Kant describe his metaphysics as the non-empirical element in the study of morality. And because we can do this, we can arrive at more certain a priori knowledge than we can when examining empirical or applied ethics. By giving his work on natural science the same kind of title, he seems to be implying the same thing with regards to natural science, and if so, this conclusion that matter can never be destroyed, must be one that does not depend on empirical evidence and is an a necessarily true proposition like a mathematical one.

Does he consider this kind of conclusion to be a synthetic a priori proposition? And if he does, is he wrong about that?

That particular conclusion, which I provide as an example, can be found in the Metaphysical Foundations of Natural Science, Chapter 3, Proposition 2, or Section 4:542.

2 Answers 2


The only tools that Kant accepts to build synthetic a priori propositions are time and space as the forms of intuition (= Formen der Anschauung) and the categories as the basic concepts (= Begriffe). Substance is one category, see his "Critique of Pure Reason", B106.

Metaphysics deals with the possibility and existence of synthetic a priori propositions.

The passage under consideration has been analyzed by C. Fr. von Weizsäcker in his essay, and in a more general context by Peter Plaass in his book.

Weizsäcker, from the viewpoint of the philosophy of physics, attributes some weight to Kant’s “Metaphysical Foundations of Natural Science”. But Kant’s ideas do not play any role in the daily business of the working scientist.

  • I believe this book was very important for physics in Germany, although indirectly, because it of course isn't a work of physics but of philosophy. Yet due to its influences new faculties of physical sciences were created through the country (back then - numerous countries).
    – user71009
    Commented Jan 16 at 15:42
  • According to the Kant, it really shouldn't influence the scientist at all because he's doing a different project. His conclusions, however should not CONFLICT with science in the same way that while the mathematician need not concern himself with physics, mathematics and physics should align. That's my problem in the Metaphysical Foundations of Science. Kant employs empirical concepts and his metaphysical conclusions based on them do not align with actual science in the way that math does.
    – Gerry
    Commented Jan 16 at 22:46

Michael Friedman wrote a book on the topic, Kant's Construction of Nature. It is very interesting and I reccommend reading it if you're curious about Kant's work.

In short: Kant doesn't think that he can derive Newton's laws fully a priori. He assumes an empirical premise - that is, the notion of matter, and tries to re-construct it from forces in a semi-Newtonian framework, without referencing simple entities as Leibniz or Newton do (atoms, monads).

He believes that there is an important correspondence between synthetic a priori principles of the first Critique and Newton's physics and that's why the book has "metaphysics" in its name - it's supposed to be a work of critical metaphysics, the doctrinal, that is: positive, part of Kant's system. Friedman even argues the work is crucial for understanding some claims that Kant makes in the first Critique.

These principles enable us to pursue mathematical science, according to Kant, giving determinate meaning to notions related to measurement etc.

  • Yes, I do have Friedman's book and have been going through it. And yes Kant does start with empirical premises. The problem is that once one starts with an empirical premise any conclusion reached can only be tentative, like scientific conclusions. By referring to this as a metaphysics, I thought Kant was trying to reach a priori conclusions. If that was his intent, then I'm not sure he succeeded.
    – Gerry
    Commented Jan 16 at 22:50
  • @Gerry I think Kant makes it very clear in i.e. Prolegomena that he doesn't think that Newton's laws are a priori but holds that they are derived from experience. In my opinion he succeeds in what he attempts to do in the Metaphysical Foundations, that is: put the framework of the Critique to use in relation to physical sciences. He's thus, of course, limited by his framework.
    – user71009
    Commented Jan 18 at 0:18

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