The following, from The Unity of Philosophical Experience, Gilson, 1948, is an elegantly concise summation of a big part of Kant's thinking. Though just a little bit long, it's worth the trouble because the thinking is worth the effort.

"The technical language of Kant is hard to master, but it is a great help to those who have once mastered it. Let us say, therefore, with him that man has both sensibility and understanding; and that sensibility itself immediately perceives given reality through two a priori forms - space and time. These forms are said to be a priori because we do not derive them from things, but impose them on things; the forms of our knowledge of reality make it an object of knowledge, and are therefore also forms of experience itself.

"Now our understanding is similarly equipped with a priori principles, such as the notions of substance, or of causality, by which it connects the various objects given to us in space and time. These principles of understanding - the so-called categories - are no more derived from things than are space and time themselves; as Kant says, they are transcendent in respect of things; they are not drawn from experience, they make it.

"This very property of the principles of understanding, being the condition of all sensible experience, is likely to be the source of a dangerous illusion. As they can deal with really perceived objects, so can they also deal with our concepts of things, as if these concepts were themselves real things - which they are not. The transcendent nature of the principles of understanding thus becomes the source of what Kant calls the transcendental illusion. It is an illusion because, instead of connecting real objects together by means of concepts, we are then connecting concepts together by means of abstract ideas, and yet we believe that we are still dealing with things. It is a transcendental illusion because its very possibility is due to the fact that the principles of human understanding are not borrowed from any particular objects, but transcendent in respect of all possible objects.

"When applied to sensible intuitions, these principles give birth to scientific knowledge, which is the proper work of understanding; when applied to scientific concepts, they beget abstract ideas, and metaphysics, which is the proper work of reason. Thus devoid of concrete objects, metaphysics is both necessary and empty. It is necessary, because we cannot stop our understanding or prevent it from thinking in a vacuum; thus converted into reason, it will prove anything. But it is also empty, precisely because it will prove everything: that there is no God and that there is a God; that there is no soul and there is a soul; that the world has a unity and that the world has no unity.

"As soon as the principles of understanding 'transcend all the limits of experience and therefore withdraw themselves from all empirical tests,' reason is bound to become 'the battlefield of these endless controversies which is called metaphysic....

"By generalizing on Hume's observation concerning the principle of causality, he came to the conclusion that scientific knowledge would be absolutely impossible unless such principles were considered not as derived from experience, which had been Hume's mistake, but as originating in pure understanding. By thus shifting from experience to the intellectual conditions of experience, Kant hoped to achieve a three-fold result: first, to rescue science from scepticism; secondly, to rid metaphysics of its pretensions to the title of objective knowledge; third, to make it clear that though a mere illusion, metaphysics was an inevitable illusion" (230-232).
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The next step for anyone interested is the two prefaces to Kant's Critique of Pure Reason. This is along the road not to disagree with or argue with or dismiss Kant, but to attempt to understand some of his ideas, necessary for any engagement with Kant's thought.