Rationalist Empiricism. Nathan Brown

outside its parameters. When a philosophical system encounters and traverses an exception it encounters its own outside within the movement of thought, without thereby either absorbing or collapsing into that outside. What I would call an exemplary exception inhabits an extra-systemic yet intra-philosophical space, a space exterior and open insofar as it is unbounded by an envelope of conceptual systematicity, yet nevertheless determined in its contours by the edges of those philosophical systems that generate exceptions—that produce exteriorities by constituting a field of internal coherence. Such an exception is exemplary insofar as it shows what the system must exclude in order to constitute its own rule, yet it also shows what a system must somehow include by gesturing toward what it cannot. This is not a properly deconstructive analysis, but more simply an effort to show the strange appearance of two exemplary exceptions and to situate them in the structure of their exteriority. It is within such a structured yet exterior space that I want to situate rationalist empiricism.

      The exemplary exceptions I consider are classic instances: Hume’s missing shade of blue and Descartes’s wax experiment. By linking them in an unfamiliar manner, I will argue that to think these exemplary exceptions together is to think the pre-Kantian chiasmus of rationalism and empiricism—the manner in which the representative “rationalist” and “empiricist” systems of Descartes and Hume produce and traverse key counter-methodological instances that can be thought within the space of methodological exteriority they inhabit.

      EXEMPLARY EXCEPTIONS

      In the texts of Descartes and Hume, both the wax experiment and the missing shade of blue are explicitly identified as exemplary exceptions, and both are disavowed as deviations from the main lines of the philosophical programs pursued by these thinkers. “But I see what it is,” writes Descartes, before taking up a piece of wax, “my mind enjoys wandering off and will not yet submit to being restrained within the bounds of truth. Very well then, just this once let us give it a completely free rein, so that after a while, when it is time to tighten the reins, it may more readily submit to being curbed.”³ Hume poses the question of whether an observer, confronted with a color progression from which a single shade of blue is missing, would be able to produce an idea of this shade without having seen it. Despite his own avowal that this would violate his epistemology, Hume decides that “the instance is so particular and singular that ’tis scarcely worth our observing, and does not merit that for it alone we should alter our general maxim.”⁴ Descartes demonstrates the cognition of res extensa by “purely mental scrutiny,”⁵ but he does so by temporarily indulging his sensory perceptions “just this once.” As a speculative counterfactual to his copy theory of perceptions, a “particular and singular” instance, Hume grants the mind’s capacity to construct the idea of an unperceived shade of blue, and then he immediately dismisses this example of an idea without a corresponding impression as “scarcely worth our observing.”

      Both these exemplary exceptions effectively suspend the epistemological principles of their authors: Descartes permits himself an empirical method that interrupts the order of reasons; Hume grants himself a rationalist thesis that contradicts his theory of mind. The somewhat tenuous validity of these suspensions is suggested by the rhetorical conduct of both thinkers, who flatly assume the assent of their readers to the major premises of their respective arguments. “But does the same wax remain?” asks Descartes. “It must be admitted that it does,” he replies on our behalf; “no one denies it, no one thinks otherwise.”⁶ “Now I ask,” writes Hume, “whether ’tis possible for him, from his own imagination, to supply this deficiency, and raise up to himself the idea of that particular shade, tho’ it had never been conveyed to him by his senses?” “I believe,” he answers, “there are few but will be of opinion that he can.”⁷ So what is it to which we assent, we might ask—binding together these exemplary exceptions—when we affirm the identity and coherence of Absent Blue Wax?

      Hume’s famous text appears toward the end of Book 1 of the Treatise and is reprinted nine years later in the Enquiry without significant alteration:

      Suppose a person to have enjoyed his sight for thirty years, and to have become perfectly well acquainted with colours of all kinds, excepting one particular shade of blue, for instance, which it never has been his fortune to meet with. Let all the different shades of that colour, except that single one, be plac’d before him, descending gradually from the deepest to the lightest; ’tis plain, that he will perceive a blank, where that shade is wanting, and will be sensible, that there is a greater distance in that place betwixt the contiguous colours, than in any other. Now I ask, whether ’tis possible for him, from his own imagination, to supply this deficiency, and raise up to himself the idea of that particular shade, tho’ it had never been conveyed to him by his senses? I believe there are few but will be of opinion that he can; and this may serve as a proof, that the simple ideas are not always derived from the correspondent impressions; tho’ the instance is so particular and singular, that ’tis scarce worth our observing, and does not merit that for it alone we should alter our general maxim.⁸

      The secondary literature on this missing shade of blue—let’s call it “Absent Blue”—is dominated in equal parts by efforts at damage control (on the part of orthodox Humeans) and by hindsight (on the part of doctrinaire Kantians).⁹ The problem for those devoted to sustaining the coherence of Hume’s copy theory of perceptions is that both the Treatise and the Enquiry unambiguously posit our ability to generate an idea of Absent Blue as a “contradictory phenomenon” demonstrative of the position “that it is not absolutely impossible for ideas to go before their correspondent impressions.”¹⁰ Why then, the scholars wonder, would Hume include this “proof” in his text, given that he asserts precisely the opposite immediately before and after? Is it an elaborate instance of Humean irony? A perverse effort to achieve notoriety through the generation of a conceptual scandal? How can it be rendered consistent with the so-called copy theory of perceptions? There can be no recourse to the theory of complex ideas here, since Hume is curiously adamant that not only different colors, but different shades of the same color “each produce a distinct idea, independent of the rest.”¹¹ Within the framework of the Treatise, then, Absent Blue is well and truly a simple idea, as irreducible to a combination of other simple ideas as it is to any impression. According to Hume himself, there is thus no way for his copy theory of perception to accommodate the putative power of the mind to “raise up” such an idea, other than to accord it the status of an “exception.”

      Hence the satisfaction of the Kantian intellectual historian, for whom this exemplary exception encapsulates the difficulties encountered by empiricism pending a theory of synthetic a priori cognition. And indeed, though it is obviously not a mathematical judgment, the cognition of Absent Blue at least approximates the structure of Kant’s 7 + 5 = 12. We are given three terms—two contiguous shades and the perception of a blank between them—and we have to produce a new term on the basis of these relations. We can in no way arrive at Absent Blue by merely combining or analyzing the terms with which we are presented, just as “the concept of twelve is by no means thought merely by my thinking of that unification of seven and five.”¹² Rather, we have to go beyond the data we are granted in order to arrive at a real amplification irreducible to either analysis or experience—presumably through intuition. Kant credits Hume as the philosopher who came closest to the problem of synthetic a priori cognition, though he faults Hume for incorrectly believing he had proven the impossibility of such cognition through his analysis of causality. But perhaps the case of Absent Blue does affirm the possibility of such cognition—though, again, it is a possibility that Hume can affirm only as an exception and which he thus remains unable to theorize. For the Kantian, the anomalous status of Absent Blue in Hume’s system betokens the necessity of a transcendental idealism that would obviate the illusory opposition of rationalism and empiricism of which such an anomaly is symptomatic.

      For anyone who seeks to obviate that opposition in a manner irreducible to transcendental critique, however, Hume’s exemplary exception opens a different opportunity for thought: the possibility of constructing a rapprochement between rationalism and empiricism without recourse to a transcendental subject. How is it possible to think—with Hume—the capacity of the mind to raise up such an idea while still—with