I
Michael Forster's little book, or longish essay, Kant and Skepticism (Princeton, NJ: Princeton University Press, 2008) weighs in at the flyweight level of just 86 pages of main text plus 54 pages of notes. But it also, at least potentially, packs a heavy philosophical punch. Its very challenging and important two-part overall thesis is this:
(1) The primary philosophical motivation behind Kant's Critique of Pure Reason (henceforth ‘the CPR’) in particular and the Critical philosophy in general is to respond to a Pyrrhonian radical sceptical ‘crisis’ about the nature, metaphysical status, and epistemic justification of human reason. Even though responding to Hume's sceptical empiricist analysis of the concepts of causation and causal necessity is a philosophical motivation of some importance for Kant in the construction of his own ‘reformed metaphysics’ of transcendental idealism, nevertheless it remains a secondary philosophical motivation. Furthermore, the need to respond to Cartesian ‘veil of perception’ scepticism or Berkeleyan sceptical metaphysical phenomenalism is a strictly tertiary and relatively unimportant philosophical motivation for Kant.
(2) Ultimately, Kant has no philosophically adequate response to Pyrrhonian radical scepticism about human reason when this radical scepticism is applied to the basic assumptions of Kant's own ‘reformed metaphysics’, i.e. transcendental idealism.
The book is divided into twelve chapters. In chapter 1, ‘Varieties of Skepticism’, Forster argues that the two primary motivational concerns of the CPR and the Critical philosophy are, first, to respond to scepticism and, second, to develop a reformed metaphysics, i.e. transcendental idealism. But most philosophical treatments of scepticism fail to distinguish adequately between:
(i) Cartesian ‘veil-of-perception’ scepticism or Berkeleyan sceptical metaphysical phenomenalism, and
(ii) Humean scepticism about (iia) purportedly a priori concepts such as CAUSATION and CAUSAL NECESSITY and also about (iib) the purported existence of a class of necessary and non-empirical truths falling between propositions about ‘relations of ideas’ (roughly, analytic a priori truths) and propositions about ‘matters of fact’ (roughly, synthetic a posteriori truths),
(iii) Pyrrhonian scepticism, which radically attacks human rationality itself by establishing a universal ‘equipollence’ or ‘suspension of judgment’, via showing how human reason falls inevitably into not only ordinary contradictions, but also vicious regresses like the Third Man, reflexive hyper-contradictions like the Liar, and impredicative (a.k.a. ‘vicious circle’ type) hyper-contradictions like Russell's Paradox.
Kant's own term-of-art for the hyper-contradictions generated by Pyrrhonian radical scepticism is ‘antinomies of pure reason’.
In chapter 2, ‘ “Veil of Perception” Skepticism’, Forster argues that Kant's need to respond to Cartesian veil-of-perception scepticism and Berkeleyan sceptical metaphysical phenomenalism (e.g. in the B or 1787 edition CPR's ‘Refutation of Idealism’) plays at most a tertiary and relatively unimportant role in the CPR and the Critical philosophy. ‘Transcendental arguments’ against Cartesian or Berkeleyan scepticism were, to be sure, quite significant in twentieth-century analytic neo-Kantian philosophy (e.g. in the work of P. F. Strawson, Barry Stroud, and others), but not for Kant himself.
Chapter 3, ‘Skepticism and Metaphysics (a Puzzle)’, raises two hard interpretative questions. (1) It is clear enough that in the Critique of Pure Reason Kant intends radically to criticize the ‘dogmatic’ classical rationalist metaphysics of Descartes, Spinoza, Leibniz, Wolff, and other seventeenth- and eighteenth-century philosophers. But at the same time, it is much less clear just what sort of ‘reformed metaphysics’ Kant's transcendental idealism actually is. So the first hard interpretative question is: ‘What was “metaphysics” for Kant?’ (p. 13). Did Kant accept Aristotle's dual classical definition of metaphysics as either the science of being qua being (general ontology) or the science of the first principles and causes deriving from separable forms and essences (general metaphysics), or did he have a radically new and post-classical conception of metaphysics in mind? Answering this question correctly and fully is made particularly tricky in light of the autobiographical fact that until the late 1760s or early 1770s, Kant himself was a classical rationalist metaphysician in the Leibniz-Wolff tradition, hence also himself a dogmatic slumberer.
(2) In 1783 Kant wrote in the Prolegomena to Any Future Metaphysics that thinking about Hume's sceptical empiricism (probably in 1771 or 1772) awakened him from his ‘dogmatic slumber’ and propelled him towards the critique of pure reason and transcendental idealism. But in a letter to Christian Garve in 1798, Kant also says that it was the discovery of the antinomies of pure reason, i.e. ‘an encounter with Pyrrhonian equipollence skepticism that occurred in the mid-1760s’ (p. 15), that originally awakened him from the Leibnizian and Wolffian dreams that filled his dogmatic slumber. So the second hard interpretative question is: ‘Precisely what awakened Kant from his classical rationalist dogmatic slumber and propelled him towards transcendental idealism?’ Forster's interpretative hypothesis is that it is Kant's letter to Garve which should be taken most seriously, and thus that it was the Pyrrhonian wake-up call in the mid-1760s, and not the Humean wake-up call in the early 1770s, that did the original Critical trick.
In chapter 4, ‘Kant's Pyrrhonian Crisis’, Forster further develops that thought, and argues that it was Kant's encounter with Pyrrhonian radical equipollence scepticism, in the form of the antinomies of pure reason, that primarily motivates the CPR and the Critical philosophy alike. The two-part proof of this is that Kant's ‘Dreams of a Spirit Seer of 1766 represents a crise pyrrhonienne in full bloom, and is indeed to all intents and purposes a self-consciously Pyrrhonian work’ (p. 19), and also that the famous opening paragraphs of the CPR's A or 1781 edition preface very explicitly trace the need for the critique of pure reason explicitly to the antinomies of pure reason, which in turn flow directly from dogmatic classical rationalist metaphysics. So it was in the Dreams that Kant originally awakened from his Leibnizian and Wolffian dreams.
In chapter 5, ‘Humean Skepticism’, Forster argues that
Kant's reflections in or shortly after 1772 on Hume's treatments of the concept of causal necessity and the causal principle … brought him to a deeper (though not yet final) understanding than he had achieved in his [famous 1772] letter to Herz [describing the fundamental problem of metaphysics as the cognitive-semantic problem of determining how it is possible for meaningful representations to refer to objects, and in particular how it is possible for meaningful a priori representations to do so, and prematurely announcing the imminent appearance of what was eventually published, nine years later in 1781, as the first Critique] of two major puzzles bearing on the possibility of metaphysics: a double puzzle about the existence and reference of a priori concepts, and a puzzle about the possibility of synthetic a priori knowledge. It is mainly this process that Kant has in mind when he credits Hume with having roused him from the slumber of dogmatic metaphysics and given his thought a quite new direction. (pp. 31–2)
Chapter 6, ‘Kant's Reformed Metaphysics’, tells us that Kant's new metaphysics of transcendental idealism is essentially designed to be a two-punch constructive response to Pyrrhonian scepticism and to Humean scepticism. In order to do this, according to Forster, it should satisfy two basic conditions of adequacy:
(1) It should exclude traditional metaphysics’ claims about supersensible items, since these run into Pyrrhonian equipollence problems, and instead include all and only those a priori concepts and principles pertaining by virtue of their general subject matter to the discipline of metaphysics (rather than to mathematics) which seem to be obviously legitimate in light of their perspicuity, their confirmation by experience, and their fundamentalness to common sense and natural science (e.g., the concept of cause and the causal principle). (2) It should advance these concepts and principles in such a way that they can be more fully defended against both the Pyrrhonian and the Hume-influenced sceptical problems than by that appearance of obvious legitimacy alone. (p. 34)
Following up on that claim, chapter 7, ‘Defenses against Humean Skepticism’, tells us that Kant's attempt to respond to Hume depends heavily on some special metaphysical features of transcendental idealism. According to Forster,
the thesis of transcendental idealism holds that the essential form of the objective world which we experience is contributed by our own minds (in contrast to its matter, which is given to us in sensation), this essential form comprising, on the one hand, the pure intuitions of space and time and the synthetic a priori principles of mathematics associated with them, and on the other hand, the a priori concepts of the understanding and the metaphysical synthetic a priori principles associated with them. (p. 42; Forster's italics)
These special features, in turn, enable Kant to respond to Hume's rejection of the very idea of synthetic a priori truth, as follows:
On the one hand, the fact that certain metaphysical synthetic a priori principles express aspects of the essential form of the objective realm of nature accounts for their truth. On the other hand, the idealist fact that we are responsible for our ability to know that they are there without prior investigations, and hence for the a priority of the knowledge in question. How can I know a priori (despite the non-analyticity of the claim) that, for example, every event has a cause? Because Iconstitute reality to conform with this principle. (p. 43; underlining added, italics in the original)
In chapter 8, ‘Defense against Pyrrhonian Skepticism’, Forster argues that Kant's fundamental response to Pyrrhonian radical equipollence scepticism is his general solution to the four antinomies of pure reason, based on transcendental idealism, which consists in ‘showing the apparent conflicts involved in the antinomies to be illusory’ (p. 45). In turn, says Forster, Kant thinks that the threat of Pyrrhonian radical equipollence scepticism is smoothly undermined and rebutted by means of transcendental idealism.
As can be seen, the first eight chapters are all purely exegetical. Then Forster does a neat philosophical about-face, and turns from historical-philosophical exegesis to serious sceptical criticism. More precisely, the last four chapters of the book constitute a step-by-step and essentially Pyrrhonian radical sceptical reply to Kant's anti-sceptical line of argument as Forster has spelled it out in the previous eight chapters. The four chapters gradually increase the degree of sceptical-critical severity, starting with some, as it were, critical no-brainers and ending with some, as it were, and as Forster thinks, critical killers.
Chapter 9, ‘Some Relatively Easy Problems’, poses two very easily resolved worries about Kant's new and reformed conception of metaphysics. Chapter 10, ‘A Metaphysics of Morals’, raises the following slightly more serious problem: how can there be such a thing for Kant as a ‘metaphysics of morals’ if he has so narrowly restricted his reformed metaphysics, by means of the thesis of transcendental idealism, to being an a priori theoretical science of the possibility of the human experience of natural objects and also of the possibility of those natural objects of human experience themselves? Chapter 11, ‘Failures of Self-Reflection’, raises an even more difficult problem: how can Kant consistently and coherently explain the possibility of synthetic a priori propositions without presupposing and using synthetic a priori propositions as premises in that very explanation, and thus generating a vicious regress?
Finally, chapter 12, ‘The Pyrrhonist's Revenge’, raises two maximally difficult (and for Forster, decisive) problems, as follows. Kant's new philosophical method, the critique of pure reason, and his reformed metaphysics, transcendental idealism, alike presuppose
(i) that human reasoners have veridical reflexive insight into the nature of their own cognitive activities and contents (I will call this the Reflexive Transparency Assumption), and
(ii) that pure general logic is formally consistent, formally complete, formally sound, cognitively inescapable, categorically obligatory, and rationally unrevisable (I will call this the Pure General Logic Assumption).
But each of these assumptions can be sceptically challenged by a suitably sophisticated Pyrrhonian radical sceptic. Hence Kant's entire philosophical project is shown to be inadequately grounded and open to Pyrrhonist radical sceptical equipollence.
II
It is time now for the Kantian's Revenge. More precisely, I have five critical worries about Forster's argument.
First, I think that Kant's felt need to respond to veil-of-perception scepticism was much more philosophically important and urgent than Forster admits, given the famous contemporary criticisms of the 1781 version of the CPR to the effect that Kant was himself either a Cartesian veil-of-perception sceptic (a.k.a. a ‘problematic idealist’) or a Berkeleyan sceptical phenomenalist (a.k.a. a ‘dogmatic idealist’). Indeed, responding to the charge that he himself was such a sceptic was one of Kant's two primary motivations for publishing a second edition of the CPR in 1787. (The other was to clarify and significantly revise the Transcendental Deduction of the Pure Concepts of the Understanding.)
Second, while I do agree with Forster that Kant's concern to respond to radical Pyrrhonian scepticism was one of Kant's primary philosophical motivations driving the CPR and the Critical philosophy, I do not agree that it was the primary motivation. The need to respond to Hume's sceptical empiricist analysis of causation, in my opinion, was equally primary.
This is closely connected with what I think is Forster's very Hegelian reading of transcendental idealism as subjective idealism. According to the subjective idealism reading, Kant is saying that the innate mentalistic structure of our capacities for cognition metaphysically constitutes the spatiotemporal and causal-dynamic structures of natural or physical reality. I agree that it is possible to read some texts in the A edition of the CPR and in the Prolegomena as subjectively idealistic. But this is an excessively uncharitable reading that Kant was deeply concerned to rule out in the B edition. More precisely, Kant's notorious conformity thesis (a.k.a. the ‘Copernican Revolution’ thesis) is most charitably interpreted as neither a physical-to-mental identity thesis nor a mental-to-physical logical supervenience thesis. In other words, most charitably interpreted, Kant does not hold that the mentalistic innate structures of our cognitive capacities metaphysically constitute the spatiotemporal and causal-dynamic structures of natural or physical reality. On the contrary, most charitably interpreted, and now positively put, Kant holds only that the spatiotemporal and causal-dynamic structures of natural or physical reality necessarily conform to or are necessarily isomorphic to, the mentalistic innate structures of our cognitive capacities. On this most charitable interpretation of Kant's conformity thesis, then, natural or physical reality is not itself mental, nor is it ‘nothing over and above’ the mental. On the contrary, on this most charitable interpretation of Kant's conformity thesis, it is simply part of the manifest essence of natural or physical reality to mirror the innate mentalistic structure of our cognitive faculties. In other words, natural or physical reality is essentially not alien to our minds. So necessarily, if and insofar as natural or physical reality actually exists, then if we were actually to exist, then we would be able to represent its formal structure a priori. That strong modal actualist counterfactual dependency is all the mind-dependence that is required for transcendental idealism. Rational human minds do not even have actually to exist in order for space-time and the causal dynamics of the real natural or physical world actually to exist.
When it is most charitably interpreted in this way, transcendental idealism is arguably a true metaphysics. Otherwise put, Kant took the demonstration of the truth of transcendental idealism to be equally as important as responding to Pyrrhonian radical scepticism: ‘I make bold to say that there cannot be a single metaphysical problem that has not been solved [in the CPR], or at least to the solution of which the key has not been provided’ (CPR Axiii; see also Bxiii–xiv).
Third, I think that Forster's worry about the very idea of a metaphysics of morals simply misses the mark. Here is what I think Kant's response to Forster's worry about the very idea of a ‘metaphysics of morals’ would be. It is one thing to postulate a system of objectively valid synthetic a priori alethic principles about nature or the natural or physical objects that rational human animals cognize, and it is quite another thing to postulate a system of objectively valid synthetic a priori deontic principles for the free moral self-legislation of rational human intentional agents. But if Kantian metaphysics, on its semantic side, is just a holistic or unified system of objectively valid synthetic a priori principles for rational human animals, then there can obviously be, as sub-species, both theoretical metaphysics (metaphysics of nature) and also practical metaphysics (metaphysics of morals).
Fourth, a key point in Forster's final and supposedly decisive two-part ‘revenge of the Pyrrhonist’ criticism is that Kant consistently and systematically underrates the force of Pyrrhonian scepticism and regards it as an essentially moderate and middle-scope form of scepticism, unlike Hegel, who, according to Forster, correctly regards Pyrrhonian scepticism as an essentially radical and wide-scope form of scepticism. Forster's principal evidence for this claim is a set of texts in which Kant treats classical Stoic scepticism as essentially moderate and middle-scope. But this entirely correct and fairly superficial point about Kant's anodyne historical-philosophical reading of the Stoics—a reading, Forster concedes, that is also defended by some leading experts in classical Greek philosophy, such as Michael Frede—completely overlooks the much deeper point that what Hegel is calling Pyrrhonian radical scepticism, and what Forster is treating as Pyrrhonian radical scepticism, is nothing more and nothing less than what Kant himself calls the dialectic of pure reason. But it would be highly misleading at best and outright wrong at worst to claim that Kant systematically underrates the force of the dialectic of pure reason.
Here, Forster's basic error is to think that Kant's general solution to the antinomies consists in ‘showing the apparent conflicts involved in the Antinomies to be illusory’ (p. 45; italics added). On the contrary, Kant holds that these are real conflicts of human reason: the dialectic of human reason is a natural dialectic. To be sure, all four of the antinomies depend on the false assumption that there is no fundamental ontological distinction between appearances or phenomena, and things-in-themselves or noumena. Or in other words, all four of the antinomies depend on the failure to recognize the truth of transcendental idealism. This shows that the thesis and antithesis of each antinomy are both false, and thus logical contraries, not logical contradictories. Kant also argues that the third and fourth antinomies can be reinterpreted in such a way as to make the thesis and antithesis both come out true, and thus consistent, but this requires making the transcendental idealist assumption that there is a fundamental ontological distinction between phenomena and noumena. The crucial points here for our purposes are
(1) that for Kant ‘pure general logic’ includes both analytic logic (the logic of truth) and also dialectical logic (the logic of fallacy and illusion) (CPR A60–2/B84–6),
(2) that insofar as classical rational metaphysics naturally falls into antinomy, the hyper-contradictions of pure reason really exist.
Now pure general logic is presupposed by transcendental logic, which adds ontological commitments to pure logic, and is a ‘science of pure understanding and of the pure cognition of reason, by means of which we think objects completely a priori’ (CPR A57/B81). Hence Kant's transcendental dialectical logic is a (deviant, non-classical) dialetheic logic (CPR A63–4/B88–9). In turn, during the CPR and in his Critical period more generally, Kant takes nothing in philosophy more seriously than the Pyrrhonian radical sceptical worries raised by the Antinomies, not even Hume's wake-up call, which (if I am correct) Kant takes just as seriously. And certainly Kant's 1798 letter to Garve, which Forster makes so much of in order to show (as I think, mistakenly) that it was the antinomies of pure reason that primarily awakened Kant from his dogmatic slumber and only secondarily Hume's sceptical empiricism, makes essentially the same point I am making. So it is passing strange that Forster does not see this direct connection, although, to be sure, this interpretative oversight also conveniently supports his two-part overall thesis.
Fifth, finally, and most importantly, I do also think that Kant has adequate responses to Pyrrhonian radical scepticism about (i) the vicious explanatory regress of synthetic a priori propositions, and (ii) the Reflexive Transparency Assumption and the Pure General Logic Assumption, and that Forster overlooks these responses.
(i) The worry about the vicious explanatory regress of synthetic a priori propositions is ruled out by Kant's non-proof-theoretic, or model-theoretic, cognitive semantics of synthetic a priori propositions. According to Kant, synthetic a priori propositions are explained by using the pure formal intuitions of space and time to determine by a semantic restriction a proper sub-class of all logically possible worlds, namely, the experienceable worlds, which include all and only those possible worlds in which space, time, matter, and causal dynamics inherently conform to our a priori cognitive faculties for representing them. Or as Kant puts it in the Transcendental Aesthetic of CPR, and then later in Philosophical Correspondence:
If we add the restriction (Einschränkung) of a judgment to the concept of the subject, the judgment is then unconditionally valid (gilt das Urteil alsdenn unbedingt). The proposition ‘All things are side by side in space’ is valid only under the restriction that these things be viewed as objects of our sensible intuition. If, here, I add the condition to the concept, and say: ‘All things, as outer appearances, are side by side in space,’ then this rule is valid universally and without restriction (allgemein und ohne Einschränkung). (CPR A27/B43)
This [principle of synthetic a priority] is completely unambiguously presented in the whole Critique, from the chapter on schematism on, though not in a specific formula. It is: All synthetic judgments of theoretical cognition are possible only through the relation of a given concept to an intuition. … [I]f the judgment is a priori synthetic, there must be a pure intuition to ground it. (11: 38)
In other words, in order to avoid the vicious explanatory regress of synthetic a priori judgments, Kant explains their necessary a priori truth by simply indicating or showing, by means of pure intuition and non-inferential a priori reasoning—and thereby not describing or saying, via concepts and inferential a priori reasoning—all and only the truth-making models of such propositions.
(ii) According to Kant, the worry about the Reflexive Transparency Assumption and the Pure General Logic Assumption is ruled out by showing that the Pyrrhonian radical sceptic necessarily presupposes both; hence in denying or in even merely supposing the denial of either, he both logically and pragmatically contradicts himself and thereby commits cognitive suicide.
Now Forster partially anticipates response (ii) by claiming that Kant is fully and mistakenly committed to strong classical versions of bivalence and the principle of non-contradiction, according to which
(a) there are no truth-values assignable to meaningful propositions other than true and false,
(b) no proposition whatsoever is semantically assigned both of the classical truth-values true and false (i.e., there are no ‘truth-value gluts’), and
(c) no proposition whatsoever is such that both it and its negation are true.
Theses (a), (b), and (c), when conjoined, add up to anti-dialetheism. Forster also claims that Kant's response to the Pyrrhonian radical sceptical dialetheist is just Aristotle's dogmatic assertion in the Metaphysics that anyone who seriously accepts dialetheism is incapable of rational thought, which of course presupposes the claim that Kant is an anti-dialetheist. But as I showed above, Kant's transcendental dialectical logic is a dialetheic logic. Classical rationalist metaphysicians actually do accept propositions which actually are both true and false. That is the logical and cognitive-semantic price to be paid for failing to recognize the truth of transcendental idealism.
Moreover and perhaps most importantly, Kant's clear and explicit commitment in the 1785 Groundwork of the Metaphysics of Morals to the universal law formula of the categorical imperative, i.e. ‘Act only on that maxim by which you can at the same time will that it should become a universal law’ (4: 421), shows that by the time of the 1787 or B edition of the CPR, at the very latest, Kant also accepts the minimal principle of non-contradiction:
Necessarily, not every proposition is both true and false.
This is because the formula of universal law clearly does not say that it is impossible to believe a maxim which, when generalized, yields an inconsistent principle, since such inconsistency is precisely the criterion of its being an impermissible maxim, which of course we believe all the time. This obvious fact allows for implicit belief in contradictions, and further supports Kant's commitment to dialetheism. Rather the formula of universal law clearly does say only that any maxim which can be permissibly adopted as a principle of willing must itself not yield self-inconsistent principles. And I think we can assume that at least one maxim is permissible, namely the maxim that I hereby commit myself to obeying the categorical imperative right now (e.g. in the formula of humanity as an end-in-itself formulation). So there must be at least one self-consistent principle, i.e. the universal generalization of at least that one permissible maxim. Hence it cannot be true that every proposition is both true and false, i.e. necessarily, not every proposition is both true and false, i.e. the minimal principle of non-contradiction is true. So even the Pyrrhonian radical sceptic, as a minimally rational and moral animal, presupposes and uses the minimal principle of non-contradiction, and thereby both logically and pragmatically contradicts himself when he either asserts or even supposes its denial. As Kant puts it in the Vienna Logic:
Proceeding skeptically nullifies all our effort, and it is an antilogical principle … For if I bring cognition to the point where it nullifies itself, then it is as if we were to regard all human cognition as nothing. (24: 884; italics added)
In this way, as Kant clearly sees, the fundamental problem with Pyrrhonian radical scepticism, no matter how sophisticated it might be, is that it implies logical nihilism about human reason and thereby commits cognitive suicide.
As I said at the outset, Kant and Skepticism proposes a very challenging and important two-part thesis. At the end of the day, I do think that Forster's thesis is false on both counts. Nevertheless, I do also think that this is an excellent book that is well worth thinking about long and hard afterwards, and that it will be a much-discussed contribution to Kant studies in the foreseeable future. As one of my undergraduate teachers at the University of Toronto, Emil Fackenheim, used to say of Hegel's philosophy: If this is wrong, at least it is greatly wrong.
