THE LIMITS OF SENSE AND REASON: A Line-By-Line Critical Commentary on Kant’s “Critique of Pure Reason,” #16–The Complex Question of Metaphysics.

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

#11: Axxi-xxii/GW104–105 Preface to the First (A) Edition

#12: Bviii-ix/GW106–107 Preface to the Second (B) Edition

#13: Bix-x/GW107 Preface to the Second (B) Edition

#14: Bx-xii/GW107–108 Preface to the Second (B) Edition

#15: Bxii-xiv/GW108–109 Preface to the Second (B) 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 Bxiv-xv/GW109–110 Preface to the Second (B) Edition

Metaphysics — a wholly isolated speculative cognition of reason that elevates itself entirely above all instruction from experience, and that through mere concepts (not, like mathematics, through the application of concepts to intuition), where reason thus is supposed to be its own pupil — has up to now not been so favored by fate as to have been to enter upon the secure course of a science, even though it is than all other sciences, and would remain even if all the others were swallowed up by an all-consuming barbarism. For in it reason continuously gets stuck, even when it claims a priori insight (as it pretends) into those laws confirmed by the commonest experience. In metaphysics we have to retrace our path countless times, because we find that it does not lead where we want to go, and it is so far from reaching unanimity in the Bxv assertions of its adherents that it is rather a battlefield, and indeed one that appears to be especially determined for testing one’s powers in mock combat; on this battlefield no combatant has ever gained the least bit of ground, nor has any been able to base any lasting possession on his victory. Hence there is no that up to now the procedure of metaphysics has been a mere groping, and what is the worst, a groping among mere concepts.

Now why is it that here the secure path of science still could not be found? Is it perhaps impossible? Why then has nature afflicted our reason with the restless striving for such a path, as if it were one of reason’s most important occupations? Still more, how little cause have we to place trust in our reason if in one of the most important parts of our desire for knowledge it does not merely forsake us but even entices us with delusions and in the end betrays us! Or if the path has merely eluded us so far, what indications may we use that might lead us to hope that in renewed attempts we will be luckier than those who have gone before us?



So much for the preliminaries, as to the epistemic, semantic, and ontological status(es) of logic, mathematics, and natural science or physics.

We’ve now reached the main event, the fundamental question of the Critique of Pure Reason, namely, the complex question of metaphysics, “complex” because it in fact is not a single question but instead five logically- and semantically-intertwined questions, each of which presupposes answers to some or all of the other questions:

(i) has metaphysics so far entered on the secure path of a science?,

(ii) if metaphysics has not so far entered this secure path, then why not?,

(iii) more generally, can metaphysics ever become an authentic science?,

(iv) if it’s impossible for metaphysics to become an authentic science, then is human reason itself inherently unreliable?, and finally,

(v) if metaphysics can indeed become an authentic science, thereby vindicating human reason at least to that extent, then how is this possible?

Kant’s answer to question (i) is clear and distinct: No — unlike logic, mathematics, and physics, metaphysics hasn’t become an authentic science, even despite its being older than the other sciences.

What’s gone wrong?

Classical metaphysics — and, as we already know from the A Preface, especially in its 17th and 18th century manifestation as classical Rationalist metaphysics, and more specifically in its Leibnizian-Wolffian version — is a

wholly isolated cognition of reason that elevates itself above all instruction from experience, and that [cognition] through mere concepts (not, like mathematics, through the application of concepts to intuition). (CPR Bxiv)

Furthermore, in classical Rationalist, Leibnizian-Wolffian metaphysics

reason continually gets stuck , even when it claims a priori insight (as it pretends) into those laws confirmed by our commonest experience. (CPR Bxiv, italics in the original)

The problem here, obviously enough, is that classical Rationalist, Leibnizian-Wolffian metaphysics, is inherently disconnected from human experience, by naturally but also self-stultifyingly being committed to the deeply false assumption that noumena or things-in-themselves are somehow knowable by reason alone, independently of human experience, and, correspondingly, by being also tragically committed to the antinomous method of vicious impredicative reasoning.

As we’ve already seen, those are the Kantian take-away points from the Humean skeptical Empiricist critique of classical Rationalism that struck Kant so vividly in 1770 or 1771, and also from his own earlier eye-opening investigations into the dialectical structure of classical metaphysics and especially classical Rationalist metaphysics in the mid-1760s.

Hence there’s no doubt that up to now the procedure of metaphysics “has been a mere groping, and what’s even worse, a groping among mere concepts” (bloßen Begriffen) (CPR Bxv).

Kant’s claim that classical metaphysics, and especially classical Rationalist metaphysis, has so far been “a groping among mere concepts” is the essential critical point here.

It’s also directly relevant to note that very similar critical points have been recently made about Analytic philosophy, not only in its logicist, logical empiricist, Quinean empiricist, conceptual-linguistic, and conceptual-intuitions stages in the 20th century, but also in its recent and contemporary Analytic metaphysics stage in the 1990s and first two decades of the 21st century.[i]

A “mere concept,” we’ll learn later in the CPR, is the same as an empty (leer) concept or noumenal concept, which in turn is a concept that is minimally well-formed in both a formal-syntactical and sortal sense, and also logically self-consistent, but essentially disconnected from human sensibility and actual or possible sensory intuition and all its manifestly real natural objects, hence a concept that doesn’t have empirical meaningfulness, or what Kant calls “objective validity”(objektive Gültigkeit).

Correspondingly, later in the first Critique, we’ll also learn that non-empty or substantive philosophical reasoning, and more specifically, real metaphysical reasoning, is

(i) inherently conceptual and a priori, like logic, but at the same time

(ii) synthetic a priori, objectual, and objectively valid, like mathematics and physics, yet also

(iii) non-constructive, unlike mathematics, and also

(iv) not the direct result of empirical reasoning constrained by abduction or inference-to-the-best-explanation, unlike natural science or physics, nevertheless also at the same time

(v) non-empirically abductive, and also necessarily indirectly related to abductive empirical reasoning in natural science, via what Kant calls transcendental deduction (CPR Axvi-xvii, A84–92/B116–124) and transcendental proof (CPR A782–794/B810–822).

We’ll recall that Kantian abduction, or reflecting judgment, is the same as Kantian inference to the best explanation, which is a kind of synthetic a priori (i.e., non-logical, non-empirical) reasoning using synthetic a priori subjunctive conditionals of the form,

Necessarily, if Γ, a set of propositions X1, X2, X3, … Xn, jointly constituting a general conception or theory, were to be true, then Y, another proposition that describes an actual fact, would also be true.

In turn, we’ll also recall that transcendental proof and transcendental deduction are themselves sub-species of Kantian abduction or reflecting judgment in which the antecedent of the synthetic a priori subjunctive conditional, Γ, is a partial or complete set of synthetic a priori presuppositions[II of the factual proposition Y that’s the consequent of the conditional, thereby demonstrating that Γ is either a (when the set of presuppositions is partial) or the (when the set of propositions is complete) condition of the possibility of Y.

Nevertheless, how philosophy in general and real metaphysics in particular can be adequately characterized in this fivefold way is, at this point in the first Critique, very far indeed from being obvious.

This stretch of argument and exposition then ends with a paragraph almost entirely composed of questions, whose interrogative content is captured by the fivefold complex question of metaphysics as I spelled it out above.

Later, in the B Introduction, Kant finally boils down this fivefold complex question of metaphysics into one single highly-compressed question: “How are synthetic judgments a priori possible?” (CPR B19, boldfacing in the original).


[i] See, e.g., P. Unger, Empty Ideas: A Critique of Analytic Philosophy (Oxford: Oxford University Press, 2014); S. Haack, “The Legitimacy of Metaphysics: Kant’s Legacy to Peirce, and Peirce’s to Philosophy Today,” available online HERE; and R. Hanna, “Kant, the Copernican Devolution, and Real Metaphysics,” in M. Altman (ed.), Kant Handbook (London: Palgrave Macmillan, 2017), pp. 761–789, also available online in preview HERE.

[ii] As I noted earlier in LSR, a proposition P1 is a presupposition of proposition P2 if and only if P1 must be true in order for P2 to be either true or false: so presuppositions are conditions of empirical meaningfulness, i.e., objective validity, for the propositions that presuppose those presuppositions.


Mr Nemo, W, X, Y, & Z, Monday 7 June 2021

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Mr Nemo

Mr Nemo

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