Earlier, when we discussed the nature of the external world, we didn't have the necessary foundation to ask if rational principles express the laws of this world in the same way that they express the laws of the mind. Now we'll try to solve this problem. By necessity, the mind sees all things under the form of rational judgments. But are things themselves also subject to such judgments? Do the laws of the mind have objective value? We'll examine them and find out.

For Kant, rational principles have only a subjective value. As we've already seen, he distinguishes between the a priori forms of sensibility and the categories of understanding (of which the most important is the rational principle of causality). Kant views both kinds of principles as equally subjective – as the forms under which the mind must conceive all things, thereby denaturing them. The sensory multiplicity that experience provides is confused and disordered, so we impose on it an artificial order that enables us to understand – at the cost of completely transforming the material of experience. So we ourselves construct the world that we know. Kant calls this the phenomenal world Τῶνϕαινομἐνων (of manifest things) – the world of things as they appear, which itself has no reality.

Kant doesn't deny that things exist outside the mind, of course, insisting only that we can't know them in themselves. For to know them, we must apply to them the forms of the mind – thereby distorting them.