Kant, in his Critique of Pure Reason, asserted under the influence of Hume that pure speculation or reason, whenever it ventures into a field in which it cannot possibly be checked by experience, is liable to get involved in contradictions or ‘antinomies’ and to produce what he unambiguously described as ‘mere fancies’; ‘nonsense’; ‘illusions’; ‘a sterile dogmatism’; and ‘a superficial pretension to the knowledge of everything’. He tried to show that to every metaphysical assertion or thesis, concerning for example the beginning of the world in time, or the existence of God, there can be contrasted a counter-assertion or antithesis; and both, he held, may proceed from the same assumptions, and can be proved with an equal degree of ‘evidence’. In other words, when leaving the field of experience, our speculation can have no scientific status, since to every argument there must be an equally valid counter-argument. Kant’s intention was to stop once and forever the ‘accursed fertility’ of the scribblers on metaphysics.
Popper’s summation of Kant’s Critique is in line with the mainstream view. Kant’s attack on “pure reason” was not meant as an attack on knowledge as such, but only on speculative knowledge, i.e., claims of knowledge about matters of fact that aren’t backed by evidence. As Thomas Henry Huxley put it:
The aim of the Kritik der reinen Verunft is essentially the same as that of the Treatise of Human Nature, by which, indeed, Kant was led to develop that “critical philosophy” with which his name and fame are indissolubly bound up: and, if the details of Kant’s criticism differ from those of Hume, they coincide with them in their main result, which is the limitation of all knowledge of reality to the world of phenomena revealed to us by experience.
Kant’s basic position can be summed up from the famous aphorism from the preface of the second edition of The Critique of Pure Reason: “Concepts without percepts are empty; percepts without concepts are blind.” Whatever errors and mistakes Kant may have committed in explicating and developing this seminal insight, the principle itself remains sound. Nor would even Rand necessarily have disagreed with it, even if she might have quibbled about the terms in which the principle is expressed.
An anonymous commentator in an earlier post insisted “that Kant's philosophy and Objectivism are diametrically opposed.” This is a bit of exaggeration. Even in the field of ethics, where the differences between Kant and Rand are the most striking, there are still similarities (e.g., they are both absolutists, and they both believe in “autonomy”). So would Rand have necessarily disagreed with Kant’s view that “when leaving the field of experience, our speculation can have no scientific status”?
Orthodox Objectivists (including Rand herself) have always been vague on this point. While Rand and her disciples will occasionally stress the importance of keeping one’s concepts in touch with reality and avoiding what they call “floating abstractions,” if we judge Objectivists by how they act rather than on what they say it becomes clear that they really are quite attached to the type of speculative reason that Kant (and Hume) criticizes. Rarely do Rand or Peikoff provide detailed, convincing evidence for their numerous controversial assertions. If they deign to advance any kind of argument at all, it is nearly always of a wantonly speculative and, ipso facto verbalistic nature. Rand’s entire theory of human nature is merely a speculative leap from her equally speculative defense of free will! One can hardly get more rationalistic and non-empirical than that!
To the extent that there is real difference between Rand and Kant on this issue “pure” reason, it is Kant, not Rand, that is on the side of science, truth and realism. The world is weary of philosophers who seek to determine matters of fact with logical, rhetorical, or moral constructions. The sort of “reason” that Objectivists actually practice (as opposed to vague, amorphous “reason” they theorize about and provide genuflect-like homage to) is merely a futile exercise in generating concepts without percepts. Kant and Hume were right to criticize such an approach. To the extent that this aspect of their philosophy has been influential, it has been influential for the better. Objectivism, on the other hand, would, if it exercised any influence at all on this issue, would constitute a step backwards for the human intellect.