Summary: Critique of Pure Reason (page 10)

Sensibility is defined as follows: The capacity to receive (receptivity) representations through the way in which we are affected by objects is called sensibility¹.

Meanwhile, an intuition that relates to an object through a sensation is called empirical intuition.

Let us keep in mind this notion of empirical intuition, as we will soon see how it contrasts with what Kant calls pure intuition.

Finally, in this paragraph—rich in definitions of key terms—we encounter for the first time the crucial notion of phenomenon:

The indeterminate object of an empirical intuition is called a phenomenon.

What is a phenomenon? It is important to understand this concept.

A phenomenon is that which is given to us in experience—or, more precisely, in intuition. The table upon which I write, or the sky I contemplate while walking, is given to me in an intuition. I experience them. They are phenomena.

At this point, we must recall what we stated at the very beginning of our explanation: unlike the empiricists, Kant does not consider the mind to be a kind of blank slate or neutral medium that passively receives sensations from the external world without altering them.

The mind has a form of its own, into which the object must be moulded in order to be perceived. This form is a priori, in that it precedes experience and makes it possible. We have already seen that the understanding has a form: a priori concepts, or categories.

Now, what Kant tells us in this chapter is that the other cognitive faculty—sensibility—also has an a priori form. And the very purpose of the Transcendental Aesthetic is to uncover these a priori forms:

A science of all the principles of a priori sensibility, I call transcendental aesthetics.

Meanwhile, the science that takes as its object the form of the understanding and contains the principles of pure thought is called transcendental logic.

Kant’s goal here is to identify the a priori forms of sensibility. Thus, he is not concerned with empirical intuition, but with pure intuition.

We can now fully grasp the meaning of the distinction we mentioned earlier—between empirical intuition and pure intuition. Empirical intuition deals with the content of sensation. Pure intuition concerns only the forms of sensibility—devoid of any material content derived from sensation. In pure intuition, the mind intuits only itself—that is, it deals solely with the form of its faculty of knowledge.

Kant’s method, then, is first to focus exclusively on sensibility (abstracting from anything belonging to the understanding), and then to isolate the a priori forms of sensibility—stripping away everything that belongs to sensation, until nothing remains but pure intuition and the mere form of phenomena.

The pure forms of sensibility are space and time.

Kant asks: Are space and time real entities? What exactly are they? Do they exist independently of us? Do they belong solely to the mind? Are they mere illusions?

These questions had been raised by many philosophers before him. Aristotle, for instance, inquires into the nature of place and the instant. He defines time as a number—the number of motion in relation to the before and after. Saint Augustine, in turn, reflects on time in a passage of the Confessions that has remained famous.

Kant offers a radically new answer to these long-standing questions.

He begins with a thought experiment. We can imagine an empty space from which every object has been gradually removed. However, we cannot imagine objects without space—that is, objects that are not located in space. Whenever we picture objects, we inevitably spatialise them, whether in two or three dimensions.

What can we conclude from this? This means that space is one of the a priori forms of our sensibility (or intuition). It is impossible to intuit anything without relying on the forms of our intuition. This is why we cannot imagine intuiting anything without employing space.

¹ Our translation. The references for the quotations are available in the book Kant: A Close Reading