According to Kant, the practical employment of reason shares with its speculative employment the characteristic feature that in using it we orient ourselves by an idea that lies beyond the conditions of experience. It is an idea of something unconditioned that transcends the conditions of knowledge in general. Rightly considered, however, only in the practical employment of reason does the use of an idea that brings us "to tear down" the boundaries of experience assume its real "importance."' The reason for this, according to Kant, is that only practical reason has an "unconditional" need for such an idea, whereas speculative reason does not.2 Kant calls the need for such an idea "unconditional" because a practical judgment is understood to be one that reason does not merely wish to pass, but must pass. Whether to pass this sort of judgment is not up to us to determine; we are, rather, obliged to do so. My essay deals with this necessity of passing practical judgments, which I will try to clarify. To begin, I will distinguish two different interpretations of this necessity: a metaphysical interpretation formulated by Kant, and a performative interpretation that Derrida, in particular, develops in his critical reading of Kant. I will defend Derrida's performative interpretation by showing that the metaphysical interpretation of the necessity in question attempts to establish it in an unsatisfactory manner, and actually cannot establish it at all. Reason, according to Kant, is similar to the understanding in being a power of synthesis; though whereas the understanding synthesizes intuitions under concepts, reason brings all our knowledge into a systematic unity. Reason effects this unity when it is guided by principles which Kant calls "transcendental ideas," ideas projected by reason so that it may fulfill its function of performing the synthesis. Transcendental ideas are principles by whose application we move beyond the limits of possible experience, and which "incite us to tear down all those boundary-fences,"3 They are ideas that reason "needs" in order to do its job, because it is solely by means of them that reason can obtain the possibility of orienting itself whenever it seeks to expand its sphere beyond the limits of experience, and tries to move within a space wherein sensible objects are no longer to be found, a space emptied of them.4 Yet the reality of these ideas can never be recognized by finite beings like ourselves, as "they are in no wise intended for use in experience."5 It is inconceivable, therefore, that within the bounds of our experience there could ever be a sensible object that would be "adequate," that is, would correspond to an idea of reason. In consequence, transcendental ideas never allow of any constitutive employment as supplying concepts of empirical objects, but have merely "an excellent, and indeed indispensably necessary, regulative employment, namely, that of directing the understanding towards a certain goal upon which the routes marked out by all its rules converge, as upon their point of intersection."6 Kant identifies precisely two kinds of judgment in which we use a transcendental idea: theoretical-speculative judgments and practical judgments. In the judgments they make, both speculative and practical reason require transcendental ideas. However, since they differ in their manner of employing such ideas, according to Kant, they are not entitled to defend in the same way their assertions of the reality of the transcendental ideas they each employ. With regard to disputes arising in the theoretical-speculative domain, writes Kant, reason's right to defend the claim of the reality of a transcendental idea is a limited one, permissible only when such a defense is required to fulfill a polemical purpose. Defense of the claim in polemical fashion (as distinguished from a dogmatic defense) aims to show that an opponent who denies the reality of the idea in question, and attempts to render the denial convincing and certain, fails to do so--and to show that his failure is at least as great as one's own when one asserts the contrary. …
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