Critique of Pure Reason

The importance of the distinction between the realm of appearances (phenomena) and the realm of “things in themselves” (noumena) is difficult to underestimate. Kant’s project requires a meaningful conceptual separation of the understanding from reason. He writes, “if the understanding cannot distinguish whether or not certain questions lie within its horizon, then it can never be sure of its claims and its possessions; rather, it must then count on receiving a multitude of embarrassing rebukes when (as is unavoidable) it keeps overstepping the bounds of its domain and stray into delusion and deception” (305). Therefore, it is necessary to comprehend the boundaries of the understanding. The previous section systematically dealt with its positive principles, but with the concept of the noumena Kant comes up to the boundary and attempts to explain how we are to think about what lies beyond. In short, we can’t think about them except as a problem.

One could say that categories of the understanding reside beyond experience as formal conditions of experience and that their existence is possible beyond their application to experience. Kant would disagree. Whereas categories of understanding might be logically possible outside of their empirical application, they can never be proven to be really possible except through this reference to experience. The simple fact that something is not logically impossible does not mean that it could ever actually exist. For this, a possible intuition is necessary. Experience is the point of contact for any determination of the real possibility of any concept of the understanding. This means, in turn, that all that we can understand is phenomena, or objects as they appear in experience. The understanding must remain silent regarding the existence of any objects beyond their appearance in experience. The things beyond appearance, the noumena, cannot be intuited, and therefore we can never prove that they really exist. In fact, their existence is merely problematic. In other words, “the concept of a noumenon is, therefore, only a boundary concept serving to limit the pretension of sensibility, and hence is only of negative use” (319).

The reason Kant invokes the notion of a transcendental deliberation in the following section, the “Amphiboly of Concepts of Reflection,” is also related to the general concern regarding classification and boundaries. To really understand the kinds of cognition thus far explored in the book (i.e., sensible intuition and pure understanding), it is important to know how to classify the presentations of the mind as referring to one or the other. Doing so should clarify what the understanding is capable of and why it is necessary that it always attaches itself to sensible intuition for the possible cognition of an object.

Kant explains: “Thought is not, indeed, in itself a product of the senses, and is to that extent also not limited by them; but it does not therefore have its own and pure use forthwith, without the assistance of sensibility since it is then without an object” (342). The understanding (and, as we will see, reason) extends beyond mere sensibility. We can think a priori, or before any application to sense experience, but none of these thoughts have any material (or object) without reference to experience.

For example, we can think about elephants in various situations without thinking about any actual elephant or any real-world event, but we would never have the object of thought “elephant” without some original exposure in sensible intuition to the animal. More technically, we can, for example, think about possibility or causality without reference to any actual possible thing or causal event, but we have no access to these principles without objects of experience.