IN THE FIRST part of this essay I shall give a general exposition of the role of skepticism in Kant’s critical philosophy. In the second part, I shall offer a critical assessment of the Kantian position that emerges.
The critical philosophy, as first set forth by Kant in the Critique of Pure Reason of 1781/7 (henceforth: the Critique), grew from and addresses a very complex set of philosophical concerns. But among these, two which stand out as especially central are a concern to address skepticism and a concern to develop a reformed metaphysics.
That much is widely recognized. However, it is a fundamental thesis of the present essay that these two projects belong tightly together, namely in the following sense: The types of skepticism which really originated and motivate the critical philosophy are types of skepticism that mainly threaten metaphysics;1 and conversely, what originated and motivates the critical philosophy’s reform of metaphysics is above all an aspiration to enable metaphysics to withstand skepticism.2
To amplify a little on the first of those points: Treatments of Kant have commonly been plagued, it seems to me, by two closely connected weaknesses—a failure to distinguish with sufficient care between different types of skepticism, and a (largely consequent) failure to discern the different roles that different types of skepticism played in connection with the origination and motivation of the critical philosophy. For the purposes of interpreting Kant, it is especially important to distinguish between the following three sorts of skepticism: First, there is “veil of perception” skepticism, or skepticism concerning the legitimacy of inferring from the existence and character of one’s mental representations to the existence and character of a mind-external world (this tends to be the very paradigm of skepticism for most Anglophone philosophers). “Veil of perception” skepticism is not especially targeted at the claims of metaphysics (though they are among its targets). Second, there is Humean skepticism, or skepticism concerning (1) the existence of concepts not derivable from corresponding sensible impressions (in Kant’s idiom: a priori concepts), and (2) knowledge of propositions neither true simply in virtue of logical law nor known from experience (in Kant’s idiom: synthetic a priori knowledge). Both of these forms of Humean skepticism are exemplified in Hume’s treatment of causation. This Humean type of skepticism does have a special bearing on metaphysics due to the prevalence of such putative concepts and such putative knowledge within metaphysics. Third, there is Pyrrhonian skepticism, a skepticism which, in the manner of the ancient Pyrrhonists, motivates suspension of judgment by establishing a balance of opposing arguments, or “equipollence” (isostheneia). As Kant interprets it, this ancient form of skepticism too has a special bearing on metaphysics.
It turns out, I shall argue, that of these three types of skepticism, the first, “veil of perception” skepticism, played no significant role at all in the origination of the critical philosophy and only a secondary role in its mature motivation (despite the fact that it is already present in the first edition of the Critique and rises to some prominence in the second edition). The second type, Humean skepticism, did play an important role in originating the critical philosophy, in virtue of its special bearing on the tenability of metaphysics, namely some time in or shortly after 1772, and also remained central to the critical philosophy’s mature motivation (facts reflected in Kant’s famous remarks about it near the start of the Prolegomena to Any Future Metaphysics of 1783 [henceforth: Prolegomena]). But it was actually the third type, Pyrrhonian skepticism, which, again in virtue of a perceived special bearing on metaphysics, first really shook Kant’s faith in the precritical discipline of metaphysics, namely in the mid-1760s, and thence eventually led to the reform of metaphysics undertaken by the critical philosophy, and which (like Humean skepticism) also remained at the heart of the mature motivation of the critical philosophy.
In its first and third parts, this interpretation will strike many scholars of Kant, especially in the Anglophone tradition, as heresy (or worse).3 This is one reason why it has seemed to me to be worth articulating.
To amplify a little on the second point made above (that what originated and motivates the critical philosophy’s reform of metaphysics is above all an aspiration to enable it to withstand skepticism): I shall argue that the key features which define the distinctive character of the reformed metaphysics at which Kant ultimately arrives in the critical philosophy—including, not only its specific conceptual and propositional contents, but also its status as a priori rather than supersensuous, its status as transcendentally ideal, and its systematicity—are all built into it mainly in order to enable it to withstand skepticism. And I shall argue that Kant has in the critical philosophy an elaborate set of strategies dependent on these features for actually defending his reformed metaphysics against skepticism.4