Summary: Critique of Pure Reason (page 7)

To acquire knowledge, it is not enough to passively experience the world (this is the naïve conception of knowledge). Instead, we must organise our experiences, provoke them, and analyse them according to our a priori knowledge.

This marks a departure from a naïve conception of knowledge—the one we tend to adopt spontaneously.

Kant describes this shift towards a more refined understanding of knowledge as follows:

Until now, it was assumed that all our knowledge had to conform to objects; yet all attempts to determine something a priori about them through concepts—something that would expand our knowledge—failed under this assumption. Let us therefore attempt, just once, to see whether we might not achieve better results in the problems of metaphysics if we assume that objects must conform to our knowledge¹.

This represents a kind of reversal: it is not our knowledge that must conform to objects, but rather objects that must conform to our knowledge (or more precisely, to our a priori concepts) in order to be known—that is, in order to become objects of knowledge.

This reversal is reminiscent of the shift introduced by Copernicus in astronomy: it is not the sun that revolves around the observer, but rather the observer who revolves around the sun.

This is a fundamental principle in Kant’s philosophy: to grasp this is to grasp the very project of the Critique of Pure Reason as a whole. Unfortunately, what we have just explained only provides a preliminary understanding.

For now, let us hold onto this preliminary understanding and note that, according to Kant, this reversal is entirely successful—it demonstrates that with this cognitive faculty, we can never go beyond the limits of possible experience.

At this point, our reading of the second Preface must be interrupted. What follows contains numerous references to ideas that will only be clarified later. We can now return to the continuation of the Introduction, having better equipped ourselves for the discussion.

We now understand what Kant is referring to when he speaks of forms of knowledge that abandon even the domain of all possible experience […] and appear to extend the scope of our judgements beyond all limits of experience: metaphysics.

The objects of metaphysical inquiry—the problems of pure reason—can, in summary, be reduced to God, freedom, and immortality.

Metaphysical reflections can neither be confirmed nor refuted by experience. Thus, we are given the impression that our knowledge can expand indefinitely, since nothing stands in the way to contradict us. This inspires Kant to use the following metaphor:

The light dove, in free flight, cleaving the air whose resistance it feels, might imagine that it would fare even better in empty space.

But this is an illusion: the air may indeed present a resistance to the dove’s flight, yet it is also its very condition—by offering resistance, it supports the dove. In the same way, experience both grounds knowledge and limits it (by refuting any theory that falsely claims the status of knowledge).

Take Plato, for instance: his theory of the world of Ideas is not based on any experience, since discovering this world requires abandoning the experience of the sensible world altogether. Yet in doing so, he merely ventures into the empty space of pure understanding, and he failed to notice that, despite all his efforts, he was making no progress at all, for he encountered nothing to oppose him, nothing that could, so to speak, provide him with a point of support.

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