THE LIMITS OF SENSE AND REASON: A Line-By-Line Critical Commentary on Kant’s “Critique of Pure Reason,” #11–Kant’s Unfinished Metaphysics of Nature, & Four Serious Problems about CPR.

By Robert Hanna


[I] was then making plans for a work that might perhaps have the title, “The Limits of Sense and Reason.” I planned to have it consist of two parts, a theoretical and a practical. The first part would have two sections, (1) general phenomenology and (2) metaphysics, but this only with regard to its method. (Letter to Marcus Herz, 21 February 1772 [C 10: 129])



Previous Installments:

#1: Introduction to The Limits of Sense and Reason

#2: Bii/GW91 The Motto

#3: Aiii/Biii/GW93–97 The Dedication

#4: Avii-ix/GW99 Preface to the First (A) Edition.

#5: Axi note/GW100–101 Preface to the First (A) Edition

#6: Axi note/GW100–101 Preface to the First (A) Edition

#7: Axii-xiv/GW101–102 Preface to the First (A) Edition

#8: Axv-xvi/GW102–103 Preface to the First (A) Edition

#9: Axvi-xvii/GW103 Preface to the First (A) Edition

#10: Axvii-xx/GW103–104 Preface to the First (A) Edition

A Note on References to Kant’s Works


The first five installments in this series followed the 2019–2020 version of THE LIMITS OF SENSE AND REASON, aka LSR.

Starting with installment #6, subsequent installments follow the revised and updated 2021 version of LSR.

In any case, you can read or download a .pdf of the complete text of the 2021 version of LSR HERE.

Because LSR is an ongoing and indeed infinite task, revised and updated .pdfs of the complete text will be uploaded to that URL on a regular basis.


CPR TEXT Axxi-xxii/GW104–105 Preface to the First (A) Edition

Axxi Such a system of pure (speculative) reason I hope myself to deliver under the title Metaphysics of Nature, which will not be half so extensive but will be incomparably richer in content this critique, which had first to display the sources and conditions of its possibility, and needed to clear and level a ground that was completely overgrown. Here I expect from my reader the patience of a judge, but there I will expect the cooperative spirit and assistance of a fellow worker; for however completely the principlesa of the system may be expounded in the critique, the comprehensiveness of the system itself requires also that no derivative concepts should be lacking, which, however, cannot be estimated a priori in one leap, but must be gradually sought out; likewise, just as in the former the whole synthesis of concepts has been exhausted, so in the latter it would be additionally demanded that the same thing should take place in respect of analysis, which would be easy and more entertainment than labor.

I have only a few more things to remark with respect to the book’s printing. Since the beginning of the Axxii printing was somewhat delayed, I was able to see only about half the proof sheets, in which I have come upon a few printing errors, though none that confuse the sense except the one occurring at page [A] 379, fourth line from the bottom, where specific should be read in place of skeptical. The Antinomy of Pure Reason, from page [A] 425 to page [A] 461, is arranged in the manner of a table, so that everything belonging to the thesis always continues on the left side and what belongs to the antithesis on the right side, which I did in order to make it easier to compare proposition and counter-proposition with one another.

a Principien



Up to this point, one might easily have been forgiven for thinking that CPR, weighing in at the super-heavyweight level of 800+ pages, would present a complete real metaphysical system of transcendental idealism.

But actually, the CPR is only a demonstration of “the sources and conditions of its possibility” of such a real metaphysics, and a negative ground-clearing exercise.

Kant says here that he does, however, intend eventually to present such a system under the title Metaphysics of Nature.

The basic idea is that the critique of pure reason will present the basic principles of the system of the metaphysics of nature, via the exhaustive synthesis of all its basic concepts, whereas the real metaphysical system itself, as comprehensive, would add all the relevant “derivative” concepts, and engage in the analysis of the basic and derivative concepts.

Kant published an essay on logic, “The False Subtlety of the Four Syllogistic Figures,” in 1762, and lectured regularly on logic from the 1760s to 1800.

In the 1800 Jäsche Logic[i] — Kant’s logic lectures, as compiled and edited by G.B. Jäsche — we learn that the cognitive activity of conceptual “synthesis” is one of assembly or putting-together, i.e., cognitive composition, whereas the cognitive activity of conceptual “analysis” is one of disassembly or taking-apart, i.e., cognitive decomposition.

Each concept is an organized mereological totality, or structured whole, consisting in an assembly of elements, or proper parts, called “marks” or Merkmale.

Marks, in turn, are general representations of attributes or properties of things.

Each concept is thus logically and semantically complex in a mereological sense, and it includes a finite system of marks organized either

(i) “vertically” into a hierarchy of “lower” concepts (determinates) and “higher” concepts (determinables), such that

(ia) every higher concept (determinable) is intensionally contained in all its determinates,

(ib) every lower concept is intensionally contained under all its determinables,

(ic) the comprehension of every higher concept set-theoretically contains the comprehensions of all its lower concepts, and

(id) the comprehension of every lower concept is set-theoretically contained by the comprehensions of all its higher concepts, or else

(ii) “horizontally” into a set of partially overlapping and partially non-overlapping concepts.

In this way, most marks are themselves “mini-concepts.”

The only basic difference between marks and concepts is that whereas every concept is a logically and semantically complex finite system of marks that can be analytically decomposed into its constituent marks, at least some marks are primitive and cannot be decomposed into any more basic logico-semantic elements.

According to Kant, synthesizing concepts clearly requires more cognitive effort than analyzing concepts, since it would be “easy and more entertainment than labor” (CPR Axxi) to provide a decomposition of the basic and derivative concepts of his metaphysics of nature, than to compose them, which presumably by contrast would be not easy and less entertainment than labor.

Easy and entertaining, or not, in the event, Kant never did produce a metaphysics of nature.

The Metaphysical Foundations of Natural Science from 1786 was clearly a beginning of it; and the unfinished Transition project from the late 1790s, the drafts and notes for which are collected in the Opus postumum, was equally clearly a final attempt at it.

In the B edition Preface in 1787, however, Kant is still officially committed to doing a metaphysics of nature, along with a metaphysics of morals (CPR Bxlii-xiv).

But there he also implies that he has “become involved in controversies” surrounding CPR, and that

since during these labors I have come to be rather advanced in age (this month I will attain my sixty-fourth year), I must proceed frugally with my time if I am to carry out my plan of providing the metaphysics of both nature and morals, as confirmation of the correctness of the critique both of theoretical and practical reason; and I must await the illumination of those obscurities (Dunkelheiten) that are hardly to be avoided at the beginning of this work, as well as the defense of the whole, from those deserving men who have made it their own. (CPR Bxliii-xliv)

In other and fewer words, he ran into vigorous criticism of CPR, and correspondingly, into some unanticipated serious philosophical problems about its main theses and arguments, after publishing the A edition.

One of these serious problems, as we have already seen, is the unclarity of the Transcendental Deduction of the Categories in the A edition, and its unsoundness in either the A or B edition, or indeed in any possible edition, namely, The Gap.

Another serious problem is the worry that Kant’s transcendental idealism entails either Cartesian external world (aka “veil-of-perception”) skepticism or Berkeleyan skeptical subjective idealism.

A third serious problem is the worry is that Kant cannot provide an adequate justification of either The Reflexive Transparency Assumption or The Pure General Logic Assumption.

But the fourth, and the most serious, problem is that Kant’s attempt to provide a positive metaphysical solution to the Third Antinomy of Pure Reason concerning freedom and natural determinism, ultimately fails.

This fourth problem is truly the most serious, because Kant’s moral theory presupposes this positive metaphysical solution.

So if that solution fails, then, assuming that no other solution can be found, it follows that there is no real freedom of the will in a deterministic manifestly real natural world and Kant’s moral theory ultimately fails too.

Curiously, most 21st century Kantian ethicists are also classical compatibilists and soft determinists, who hold

not only (i) that free will and universal natural determinism are metaphysically consistent (classical compatibilism),

but also (ii) that universal natural determinism is true although our rich moral psychology stubbornly tells us that we are non-deterministically free (soft determinism), and,

curiouser and curiouser, (iii) that Kant’s attempted transcendental idealist metaphysics of source-incompatibilist, non-deterministic free will, by way of a positive metaphysical solution to the Third Antinomy, actually fails.

Therefore, self-stultifyingly, these contemporary Kantian ethicists must also hold that Kant’s moral theory actually fails.

But that, surely, is what Kant himself would have called “a scandal of philosophy and universal human reason” — as per CPR Bxxxix n., where he applies that damning epithet to previous philosophers’ failures to refute Cartesian problematic idealism — that could be rectified only as follows:

first, by developing and defending a contemporary Kantian transcendental idealist metaphysics of source-incompatibilist, non-deterministic free will,[ii]

and then and only then,

second, proceeding with contemporary Kantian ethics.[iii]


[i] See, e.g., R. Hanna, “Jäsche Logic,” in J. Wuerth (ed.), Cambridge Kant Lexicon (Cambridge: Cambridge Univ. Press, 2021), pp. 707–711, available online in preview HERE.

[ii] See, e.g., R. Hanna, Deep Freedom and Real Persons: A Study in Metaphysics (THE RATIONAL HUMAN CONDITION, Vol. 2) (New York: Nova Science, 2018), also available online in preview HERE.

[iii] See, e.g., R. Hanna, Kantian Ethics and Human Existence: A Study in Moral Philosophy (THE RATIONAL HUMAN CONDITION, Vol. 3) (New York: Nova Science, 2018), also available online in preview HERE.


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Formerly Captain Nemo. A not-so-very-angry, but still unemployed, full-time philosopher-nobody.

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