Kant's theory of perception
Main articles: The Critique of Pure Reason and Transcendental Doctrine of Elements
Kant defines his theory of perception in his influential 1781 work The Critique of Pure Reason, which has often been cited as the most significant volume of metaphysics and epistemology in modern philosophy. Kant maintains that our understanding of the external world has its foundations not merely in experience, but in both experience and a priori concepts – thus offering a non-empiricist critique of rationalist philosophy, which is what he and others referred to as his "Copernican revolution."[18]

Before discussing his theory, it is necessary to explain Kant's distinction between analytic and synthetic propositions.

Analytic proposition: a proposition whose predicate concept is contained in its subject concept; e.g., "All bachelors are unmarried," or, "All bodies take up space."
Synthetic proposition: a proposition whose predicate concept is not contained in its subject concept ; e.g., "All bachelors are happy," or, "All bodies have mass."
Analytic propositions are true by nature of the meaning of the words involved in the sentence - we require no further knowledge than a grasp of the language to understand this proposition. On the other hand, synthetic statements are those that tell us something about the world. Synthetic statements are true or false because their meaning transcends the content of the language used. In this instance, mass is not a necessary predicate to the body; until we are told the heaviness of the body we do not know that it has mass. In this case, experience of the body is required before its heaviness becomes clear. Before Kant's first Critique, empiricists (cf. Hume) and rationalists (cf. Leibniz) assumed that all synthetic statements required experience in order to be known.

For more details on this topic, see Analytic-synthetic distinction.
Kant, however, contests this: he claims that elementary mathematics, like arithmetic, is synthetic a priori. Here Kant includes a priori and a posteriori concepts into his argument, and posits that it is in fact possible to have knowledge of the world that is not derived from empirical experience. Thus does Kant develop his arguments for transcendental idealism. He justifies this by arguing that experience depends on certain necessary conditions - which he calls a priori forms - and that these conditions hold true for the world. In so doing, his main claims in the " Transcendental Aesthetic" are that mathematic judgments are synthetic a priori and in addition, Space and Time are transcendentally ideal and at the same time are necessary conditions for experience.

For more details on this topic, see A priori and a posteriori (philosophy).
This is quite naturally confusing, yet Kant's idea is that since his first claim — about mathematic judgments — is true, then it will follow that his claims about space and time are true as well. The next paragraph deals with the notion of mathematic judgments being synthetic a priori, skip to the paragraph afterward to read more about perception and Kant.

Once we have grasped the concepts of addition, subtraction or the functions of basic arithmetic, we do not need any empirical experience to know that 100 + 100 = 200, and in this way it would appear that arithmetic is in fact analytic. However, that it is analytic can be disproved thus: if the numbers five and seven in the calculation 5 + 7 = 12 are examined, there is nothing to be found in them by which the number 12 can be inferred. Such it is that "5 + 7" and "the cube root of 1,728" or "12" are not analytic because their reference is the same but their sense is not - meaning that the mathematic judgment "5 + 7 = 12" tells us something new about the world. It is self-evident, and undeniably a priori, but at the same time it is synthetic. And so Kant proves a proposition can be synthetic and known a priori.

For more details on this topic, see Sense and Reference.
Kant asserts that perception is based both upon experience of external objects and a priori knowledge. The external world, he writes, provides those things which we sense. It is our mind, though, that processes this information about the world and gives it order, allowing us to comprehend it. Our mind supplies the conditions of space and time to experienced objects. According to the "transcendental unity of apperception", the concepts of the mind (Understanding) and the intuitions which garner information from phenomena (Sensibility) are synthesized by comprehension. Without the concepts, intuitions are nondescript; without the intuitions, concepts are meaningless — thus the famous quotation, "Intuitions without concepts are blind; concepts without intuitions are empty."[19]

so its basically just analytical vs. synthetic?

^What makes him crappy, in your opinion? Just curious.

^could you explain his theory?

does anyone have any other websites since my teachers won't accept wikipedia as a valid source?