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In this one pithy sentence, we find a list of many important earlymodern questions concerning space. Is space “real,” or isit “ideal” in some sense? Is it a substance in its ownright, a property of some substance, or perhaps neither? Is it somehowdependent on the relations among objects, or independent of thoserelations? What is the relationship between space and the mind? Andfinally, how do these various issues intersect with one another?
Finally, transcendental idealism, in so far as it concerns space andtime, has the following essential component: we have a non-empirical,singular, immediate representation of space. Part of Kant’s innovationis to introduce into the philosophical lexicon the very idea that wecan have non-empirical intuition. It is improbable that we caninterpret this idea correctly unless we remind ourselves that Kantrigorously distinguishes between sensation and intuition. Thatdistinction, in turn, forms a crucial component in Kant’s extensiverejection of the Leibnizian doctrine of perception. It is only withthe rejection of that doctrine that we can understand Kant’s breakwith the Leibnizian view of space and time in the right light.
Ironically, the view that Kant is—perhaps despite his ferventdenials—an idealist of the Berkeleyan variety arose in one ofthe first critical appraisals of the Critique, the so-calledGarve-Feder review of 1782.In the Prolegomena, written directly after the review, Kant isconcerned to distinguish his version of idealism from Berkeley’s; onepoint he emphasizes hinges on their differing conceptions of space. Inconsidering the question of why his early critics Garve and Federinterpreted him as a Berkeleyan idealist, he writes:
We have seen above that from Kant’s point of view, both Leibniz andNewton—and perhaps some of their followers—defend versionsof “transcendental realism.” This is due to their supportof the view—or perhaps commitment to the view (on othergrounds)—that space and time are independent of intuition insome sense. They may also be adherents of this realist position on thegrounds that they do not articulate the view Kant defends in theMetaphysical Exposition, viz. that we have a non-empirical, singular,immediate representation of space and time. But what does it mean forKant to say that space and time are somehow dependent on intuition?One way of achieving some clarity in this domain is to fill out whatKant regards as the relevant conceptual landscape by looking to hischaracterization of another idealist position, that of Berkeley (as heunderstands him). So suppose that space is not a property of objectsindependent of intuition in any sense—it does not evensupervene on properties of objects that are independent ofintuition (recall that for Leibniz, space supervenes on the monadicorder because objects and relations supervene on that order). On theview I want to consider, space does not supervene on properties ofobjects that are independent of intuition because there are no suchproperties. Suppose that space is indeed dependent on intuition, buton empirical intuition. I take this to represent onepossible construal of Berkeley’s phrase, esse estpercipii. This consideration suggests that, prima facie,Kant should not interpret Berkeley as a transcendental realist. And ifthat is right, what prevents Berkeley from being understood as atranscendental idealist? Correlatively, what prevents one fromunderstanding transcendental idealism as some kind of Berkeleyanidealism about space and time? These sorts of question can help toclarify what Kant understands by transcendental idealism, forKant seems to view Berkeley as a fellow idealist, but one who does notdefend a transcendental variety of this position.
Transcendental idealism is obviously too complex to clarify simply bydiscussing Kant’s views of space and time. A full discussion of itwould have to range over his critical writings in metaphysics,aesthetics, teleology, and ethics. But as we have seen, Kant himselfindicates in the Transcendental Aesthetic that transcendental idealismis closely related to his conception of space and time, and so someclarity concerning Kant’s overarching philosophical position can beachieved in the context of this entry. The modus operandi, asabove, will be to probe Kant’s own discussions of the views of spaceand time articulated by his predecessors in order to clarify his ownposition. In particular, Kant’s remarks concerning Berkeley areespecially helpful in this context, in addition to his remarks onLeibniz and Newton.
Friedman has modified his original position in response tocriticism from Emily Carson (Carson 1997), who has developed aninterpretation of Kant's theory of geometry that is Parsonsian in itsanti-formalist emphasis on the epistemological and phenomenologicalover the logical role for intuition in mathematics. In recent work(Friedman 2000, 2010), Friedman argues that the intuition that groundsgeometry is fundamentally kinematical, and is best explained by thetranslations and rotations that describe both the constructive actionof the Euclidean geometer and the perceptual point of view of theordinary, spatially oriented observer. This new account provides asynthesis between the logical and phenomenological interpretiveaccounts, in large part by connecting the geometrical space that isexplored by the imagination via Euclidean constructions to theperspectival space that is, according to Kant, the form of all outersensibility. More specifically, he reconciles the logical with thephenomenological by “[embedding] the purely logicalunderstanding of geometrical constructions (as Skolem functions)within space as the pure form of our outer sensible intuition (asdescribed in the Transcendental Aesthetic)” (Friedman 2012,n.17).
Michael Friedman's original position (Friedman 1985, 1992) withrespect to the role of intuition in mathematical reasoning descendsfrom Beth's and Hintikka's, though it is substantially different fromtheirs and has been modified in his most recent writings. Inhis Kant and the Exact Sciences (Friedman 1992), Friedmantakes the position that our modern conception of logic ought to beused as a tool for interpreting (rather than criticizing) Kant, notingthat the explicit representation of an infinity of mathematicalobjects that can be generated by the polyadic logic of modernquantification theory is conceptually unavailable to the mathematicianand logician of Kant's time. As a result of the inadequacy of monadiclogic to represent an infinity of objects, the eighteenth-centurymathematician relies on intuition to deliver the representationsnecessary for mathematical reasoning. Friedman explicates the detailsof Kant's philosophy of mathematics on the basis of this historicalinsight.
Kant wishes to oppose this Leibnizian attitude towardsensibility—which he goes on to label an “entirely unjustperspective” (A44/B62)—in a general but thoroughgoing wayin the Aesthetic and elsewhere in the Critique. In theAmphiboly, for instance, he complains that Leibniz “left nothingfor the senses but the contemptible job of confusing and upsetting therepresentations” of the understanding (A276/B332). Thus Kantdoes not merely think that we have a non-empirical, singular,immediate representation of space. He thinks—if we borrowLeibnizian terminology—that our clear and distinctrepresentation of space is singular and immediate. For Kant, intuitioncan be a genuine source of clear and distinct representations.
We can then see the first two arguments in the Metaphysical Expositionas attempting to undermine (1), and the second two arguments asattempting to undermine (2). Thus Leibniz denies that we have an apriori, singular, immediate representation of space. Instead, hethinks we begin with an empirical representation of space, remove theconfused elements of that representation, and thereby obtain a clearand distinct idea, i.e., a conceptual representation of an abstractmathematical entity.
No matter how many laps on the track of metaphysics Kant takes us through, he is still widely held as one of the greatest modern philosophers of our time....