THE LIMITS OF SENSE AND REASON: A Line-By-Line Critical Commentary on Kant’s “Critique of Pure Reason,” #13–What is “the Secure Path of a Science”?

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

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

For the advantage that has made it so successful logic has solely its own limitation to thank, since it is thereby justified in abstracting — is indeed obliged to abstract — from all objectsb of cognition and all distinctions between them; and in logic, therefore, the understanding has to do with nothing further than itself and its own form. How more difficult, naturally, must it be for reason to enter upon the secure path of a science if it does not have to do merely with itself, but has to deal with objectsc too; hence logic as a propadeutic constitutes only outer courtyard, as it were, to the sciences; and when it comes to information, a logic may indeed be presupposed in judging about the latter, but its acquisition must be sought in the sciences properly and objectively so called.

Insofar as there is to be reason in these sciences, something in them must be cognized a priori, and this cognition can relate to its object in either of two ways, either merely determining the object and its concept Bx (which must be given from elsewhere), or else also making the object actual. The former is theoretical, the latter practical cognition of reason. In both the pure part, the part in which reason determines its objectd wholly a priori, must be expounded all by itself, however much or little it may contain, and that part that comes from other sources must not be mixed up with it; for it is bad economy to spend blindly whatever comes in without being able later, when the economy comes to a standstill, to distinguish the part of the revenue that can cover the expenses from the part that must be cut.

b Objecte

c Objecte

d Object



Once we’ve properly contextualized Kant’s notorious remarks about logic, then we can clearly see that it makes very good sense for him to claim that by contrast to pure general logic, any other aspirational science will of necessity be at least partially determined by the objects and states-of-affairs belonging to its characteristic subject-matter, and correspondingly, in direct proportion to its objectual component, find it more difficult

to enter upon the secure path of science if it does not have to do merely with itself, but has to deal with objects too. (CPR Bix)

For pure general logic has its internal structure determined by the nature of theoretical rationality itself, and is necessarily underdetermined by any of the actual or possible objects to which logic applies.

But sciences other than pure general logic, which are, in a systematic way, epistemically, semantically, and metaphysically dedicated to the special sorts of objects to which they apply, will be correspondingly required to formulate their specific ends, basic principles, and epistemic methods in terms of those special sorts of objects.

I emphasize the ostensive term “those,” because for Kant, all dedicated reference to special sorts of objects is intuitional, not conceptual.

All epistemic, semantic, and metaphysical sensitivity is a function of our cognitive capacity for sensibility.

On top of that, those special sorts of objects might well be, by their very nature, more inherently difficult to know, and more inherently complicated to connect as truth-makers to the propositions that refer to them and describe them, than other sorts of objects.

As a consequence, although it’s true that given The Pure General Logic Assumption, it follows that pure general logic functions as a “propadeutic,” or necessary preliminary, to all the other sciences, and also that it’s presupposed by any truth-evaluable cognitions or judgments framed inside those sciences, nevertheless pure general logic cannot itself determine the success or failure of that aspirational science as a science.

So over and above the categorically normative but still minimal constraints and norms imposed by pure general logic, what does determine the success or failure of an aspirational science, as a science?

The short answer is that it’s all about the special sorts of objects that constitute the subject-matters of those sciences, and more precisely, all about the special epistemic, semantic, and metaphysical conditions imposed by the specific characters or natures of those special sorts of objects.

As I’ve already pointed out, according to Kant, the best possible philosophical explanation of the relationship between a priori cognitions on the one hand, and their corresponding abstract, non-empirical objects and states-of-affairs on the other, is yielded by postulating

(i) that the proper objects of rational human cognition are necessarily restricted to being manifestly real natural objects and states-of-affairs that can be presented to actual or possible human experience, and

(ii) that the essential forms of and relations between objects and states-of-affairs in the manifestly real natural world necessarily conform to the innately-specified mentalistic structures of our rational human cognitive capacities, not the other way around.

That postulate is, of course, Kant’s real metaphysics of transcendental idealism.

But even granting the thesis of transcendental idealism, there are two different ways in which rational human cognition can relate a priori to its objects:

either (i) rational human cognition “determines”(bestimmt)the forms of objects that are themselves given independently to human cognition, in which case reason’s cognition is theoretical,

or (ii) rational human cognition also “makes”(macht) its objects “actual” (wirklich) in which case reason’s cognition is practical.

One vitally important point here is that, perhaps surprisingly, Kant’s notion of cognition or Erkenntnis is not restricted to classically epistemic and theoretical contexts, but also covers practical or classically non-epistemic and non-theoretical mental acts and states.[i]

Otherwise put, the notion of cognition in Kant’s sense is essentially the same notion as intentionality, which covers both aboutness, or referential and propositional directedness to objects and also agency, or conative and volitional directedness to the performance of actions.

In view of this equivalence between Kantian cognition and intentionality, it musn’t be assumed that in drawing this distinction between theoretical reason and practical reason, Kant is saying that whereas practical reason is active vis-à-vis its objects, theoretical reason is passive vis-à-vis its objects.

On the contrary, Kant is fully committed to the metaphysical thesis that human reason is inherently spontaneous no matter what its objects might be, just as, as I pointed out in my discussion of the A Preface, he’s also fully committed to the metaphysical thesis that the human mind in all of its operations and phases is inherently alive, active, and purposive, namely, goal-directed or teleological.

This is Kant’s cognitive organicism.[ii]

Indeed, as I’ll argue later in my discussions of the Transcendental Aesthetic and Transcendental Deduction of the Pure Concepts, the inherent vitality, activity, and teleology of the human mind itself constitutes a lower-level, essentially non-conceptual or non-discursive, and proto-rational kind of spontaneity, upon which the higher-level, essentially conceptual or discursive, and specifically rational kind of spontaneity is built, and which it fully presupposes.

Nevertheless, whereas theoretical reason spontaneously representationally generates the cognitive forms to which the independently-given manifestly natural objects of human cognition necessarily conform, practical reason also actualizes the matter of these objects, and thereby “makes” or produces them, which is to say that practical reason includes theoretical reason and also has specifically causal powers to initiate, from itself, or von selbst, as an incompatibilistic ultimate source, new or unprecedented events or processes in manifestly real natural space and time.

Or in other words, via practical reason, we are not only lower-level spontaneous living and purposive subjects, and higher-level spontaneous cognitive or intentional subjects, we are also incompatibilistic agential causal sources.

This incompatibilistic agential causal sourcehood is what Kant also, much later in the first Critique calls transcendental freedom (CPR A446/B474, A448/B476, and A553/B561).

There will be much, much more to say about transcendental freedom when we reach the commentary on the Third Antinomy of Pure Reason.

For our present purposes, however, the take-away point is that not only are theoretical and practical reason alike both inherently alive, active, and purposive, hence lower-level

spontaneous, and not only are they alike both inherently discursively higher-level spontaneous, but also practical reason is itself triply spontaneous, and indeed “absolutely” causally spontaneous, via its incompatibilistic agential causal sourcehood, or transcendental freedom.

Now back to authentic science and theoretical reason.

To the extent that a given authentic science is a science of pure theoretical reason and thereby is a priori, then it contains spontaneous determinative relations to the forms of manifestly real natural objects and states-of-affairs.

The specific character of these spontaneous determinative relations must be sharply distinguished from other, material aspects of those manifestly real natural objects and states-of-affairs, since it is precisely this specific character that constitutes the apriority of that particular science, regardless of other elements or features of the science that derive from other (presumably empirical) sources.

In order to make this fairly abstract metaphysical point, however, Kant shifts to a fairly unhelpful economic analogy:

It is bad economy to spend blindly whatever comes in without being able later, when the economy comes to a standstill, to distinguish the part of the revenue that can cover the expenses from the part that must be cut. (CPR Bx)

Obscurum per obscurius: thanks for nothing!, Mr Green.[iii]

In any case, the idea here seems to be that if one attempts to explain the complete epistemic or semantic content of a science without first carefully isolating the proper part of this content that constitutes its apriority (“to spend blindly whatever comes in”), then, when the epistemic and semantic credentials of this science are critically examined and evaluated (“later, when the economy comes to a standstill”), there is no way of guaranteeing that what is being explained is the epistemic and semantic essence of that science, and not accidental or contingent elements or features of the science (“without being able …. to distinguish the part of the revenue that can cover the expenses from the part that must be cut”).

It’s a pity that Kant’s meaning here is so difficult to extract, because the rhetorical function of this important preliminary point is to set up Kant’s even more important comparative and contrastive discussion of mathematics and natural science or physics, as two bona fide authentic or successful a priori theoretical sciences, which, when compared and contrasted with pure general logic, the original or Ur-science in relation to all the other authentic sciences,

are the two theoretical cognitions of reason that are supposed to determine their objects a priori, the former entirely purely, the latter at least in part purely but also following the standards of sources of cognition other than reason (CPR Bx, boldfacing in the original),

but also specifically in relation to metaphysics, which at this point in the discussion is still taken to be only an aspirational science.

Or in other words, Kant now wants to explain precisely how it is that mathematics, as a wholly pure a priori theoretical objectual science, and natural science or physics, as an at least partially pure a priori theoretical objectual science, are both “on the secure path of science,” in order to be able to judge whether, and if so, how, metaphysics can also be a wholly or at least partially pure a priori theoretical objectual science that is also on the secure path of science.


[i] This gives rise to a minor translational confusion in contemporary philosophical English, since nowadays non-epistemic and non-theoretical contexts are often called “non-cognitive.” But Kant’s refusal to reduce the theory of cognition or Erkenntnistheorie to one of its proper parts, namely, to epistemology or the theory of knowledge (Wissen), quite apart from its other philosophical advantages, has the significant philosophical virtue of correctly retaining the cognitive or intentional component in non-epistemic or non-theoretical contexts.

[ii] See, e.g., R. Hanna, “Kant’s B Deduction, Cognitive Organicism, the Limits of Natural Science, and the Autonomy of Consciousness,” Contemporary Studies in Kantian Philosophy 4 (2019): 29–46, available online at URL = <>.

[iii] It seems likely that Kant’s frequent use of economic analogies and metaphors in the first Critique — e.g., the famous hundred thalers in his equally famous critique of the Ontological Argument — was due largely to the intellectual influence of Kant’s close friend, Joseph Green, who was a merchant. See M. Kuehn, Kant: A Biography (Cambridge: Cambridge Univ. Press, 2001). pp. 154–158, and 240–241. Sadly, Kant’s Green-inspired economic analogies and metaphors are generally more confusing than helpful.

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

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