@JLNobody,
Quote:But what about modern observational tools (i.e., extensions) of perception like x-rays, microscopes and telescopes in all their variations? Don't they give us access to things that existed but could not be sensed in Kant's time?
Leibniz was influenced by the microscopic life that early optical instruments of his era revealed. And a younger Kant even proposed (long before it was confirmed in the 1920s) that some of the hazy, gaseous clouds detected by primitive telescopes were actually other galaxies like the Milky Way. But detection of atoms and particles was certainly not available in his time.
Kant nonetheless did allow for endless new revelations concerning Nature. Anything that natural science, and mathematics working in conjunction with it, theorized about and empirically uncovered in the future was still confined to the phenomenal world (below).
K -
"In mathematics and in natural philosophy human reason admits of limits but not of bounds, viz., that something indeed lies without it, at which it can never arrive, but not that it will at any point find completion in its internal progress. The enlarging of our views in mathematics, and the possibility of new discoveries, are infinite; and the same is the case with the discovery of new properties of nature, of new powers and laws, by continued experience and its rational combination. But limits cannot be mistaken here, for mathematics refers to appearances only, and what cannot be an object of sensuous contemplation, such as the concepts of metaphysics and of morals, lies entirely without its sphere, and it can never lead to them; neither does it require them. It is therefore not a continual progress and an approximation towards these sciences, and there is not, as it were, any point or line of contact."
Things in themselves, as a counterpart to the ever-generated maze of relational interdependency in the experienced world, was where reason looked to find its completion:
K -
"Reason with all its concepts and laws of the understanding, which suffice for empirical use, i.e., within the sensible world, finds in itself no satisfaction because ever-recurring questions deprive us of all hope of their complete solution. The transcendental ideas, which have that completion in view, are such problems of reason. But it sees clearly, that the sensuous world cannot contain this completion, neither consequently can all the concepts, which serve merely for understanding the world of sense, such as space and time, and whatever we have adduced under the name of pure concepts of the understanding. The sensuous world is nothing but a chain of appearances connected according to universal laws; it has therefore no subsistence by itself; it is not the thing in itself, and consequently must point to that which contains the basis of this experience, to beings which cannot be known merely as phenomena, but as things in themselves. In the cognition of them alone reason can hope to satisfy its desire of completeness in proceeding from the conditioned to its conditions."
Albeit practical reason alone could venture there, not theoretical reason, and the former couldn't prove whatever it might conclude necessary to project upon things in themselves for the sake of freedom, morality, etc. In the
Critique of Pure Reason, Kant gave a preview or glimpse of the later
Critique of Practical Reason with passages like this:
K -
"But when all progress in the field of the supersensible has thus been denied to speculative reason, it is still open to us to enquire whether, in the practical knowledge of reason, data may not be found sufficient to determine reason's transcendent concept of the unconditioned, and so to enable us, in accordance with the wish of metaphysics, and by means of knowledge that is possible a priori, though only from a practical point of view, to pass beyond the limits of all possible experience. Speculative reason has thus at least made room for such an extension; and if it must at the same time leave it empty, yet none the less we are at liberty, indeed we are summoned, to take occupation of it, if we can, by practical data of reason. This attempt to alter the procedure which has hitherto prevailed in metaphysics, by completely revolutionising it in accordance with the example set by the geometers and physicists, forms indeed the main purpose of this critique of pure speculative reason. It is a treatise on the method, not a system of the science itself. But at the same time it marks out the whole plan of the science, both as regards its limits and as regards its entire internal structure."
First two quotes from Sect. 57 of
Prolegomena To Any Future Metaphysics; Paul Carus translation. Last quote from
Critique of Pure Reason, p24-25, Norman Kemp Smith translation
