Summary: Critique of Pure Reason (page 2)

Without these pure concepts of the understanding, no experience would be possible. No object would appear to us. They are the conditions of all possible experience. They are not, therefore, formed through experience; rather, it is thanks to them that experience itself is formed. This is why they are a priori concepts.

There is thus a set of a priori concepts that constitute the form of our understanding—something the empiricists failed to recognise.

This distinction allows us to conceive of two types of knowledge: empirical knowledge and a priori knowledge. Indeed, the first paragraph of the Introduction is dedicated to distinguishing between them.

Kant concedes to the empiricists that all our knowledge begins with experience¹. It is experience—specifically, that of objects affecting our senses—that awakens our cognitive faculties.

However, this is only true in a chronological sense. Certainly, no knowledge precedes experience within us, and all knowledge begins with it. But this does not mean that experience is the cause of all our knowledge. It is important to distinguish between cause and origin:

Even though all our knowledge starts with experience, it does not necessarily follow that it is entirely derived from experience.

Indeed, if the understanding has a form of its own, it is possible that what we experience (for instance, the sight of an external tree) is not the thing itself in its true nature, but rather the thing as modified by the understanding in order to become an object of experience, conforming to its form.

In other words, it is a mixture, a compound of what the thing is in itself and what the understanding has added to it in order for it to be an object of possible experience:

It may well be the case that even our experiential knowledge is a composite of what we receive through impressions and what our own cognitive faculty [...] produces of itself.

Let us take another example: when we wear dark sunglasses to protect ourselves from the sun, we no longer see reality as it is. The dark lenses distort the colours, making them appear darker. While allowing us to see the world, the sunglasses also alter it.

In the same way, the understanding enables us to relate to and think about the things of the external world, but in doing so, it irreversibly modifies them. The categories of quantity, quality, and so on are introduced into them. We believe that these categories belong to the things themselves, whereas in reality, it is we who project them onto things—they belong only to the mind.

Just like sunglasses, the understanding allows us to apprehend the world, while at the same time distorting it.

An interesting idea has now emerged: in addition to empirical knowledge, there would be another type of knowledge—a priori knowledge—which concerns these a priori (or pure) concepts of the understanding:

This is a question that requires closer examination than that of whether there is such knowledge, independent of experience and even of all sensory impressions.

Several questions arise: what would such knowledge look like? Do sciences of this kind already exist? How can we distinguish a priori knowledge from empirical knowledge?

Kant provides an essential criterion that allows us to identify a priori knowledge with certainty: an a priori judgement is characterised by its necessity and universality.

Since Hume, it has been understood that experience cannot serve as a basis for universal and necessary laws. Experience teaches me that the sun has always risen, but it does not allow me to infer from this empirical fact that it will always rise in the future.

Likewise, all the swans I have seen so far have been white, but I cannot deduce from this the law that all swans are white. It is always possible that a future experience could contradict past experiences. Indeed, black swans were eventually discovered.

By contrast, an a priori judgement always constitutes a universal and necessary law:

Necessity and strict universality are thus reliable criteria of a priori knowledge, and they are inseparably linked to one another.

But do such universal and necessary laws truly exist? What examples of a priori judgements does Kant provide?

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