Dogmatic Slumber:Before Kant, David Hume accepted the general view of rationalism about a priori knowledge. However, upon closer examination of the subject, Hume discovered that some judgments thought to be analytic, especially those related to cause and effect, were actually synthetic meaning no analysis of the subject will reveal the predicate. They thus depend exclusively upon experience and are therefore a posteriori. Before Hume, rationalists held that effect could be deduced from cause; Hume argued that it could not and from this inferred that nothing at all could be known a priori in relation to cause and effect. Kant, who was brought up under the auspices of rationalism, was deeply disturbed by Hume's skepticism. Kant explains that Hume stopped short of considering that a synthetic judgment could be made 'a priori'. Kant's goal was to find some way to derive cause and effect without relying on empirical knowledge. He rejected analytical methods for this, arguing that analytic reasoning cannot tell us anything that is not already self-evident. Instead, Kant argued that it would be necessary to use synthetic reasoning.

Copernican RevolutionInstead of an outside-in approach to knowledge of the empiricists, in which objects cause passive perceivers to have “sensations” (Locke) or “impressions” (Hume), Kant said that the categories of space and time (forms of intuition) were imposed on experiences by the human mind in order to make sense of it. Kant called this his “Copernican Revolution.” Just as Copernicus rejected the idea that the sun revolved around the earth, Kant had solved the problem of how the mind acquires knowledge from experience by arguing that the mind imposes principles upon experience to generate knowledge. The "Copernican Revolution" of Kant introduced the human mind as an active originator of experience rather than just a passive recipient of perception. The mind is not a blank slate, perceptual input must be processed or it would just be noise and mean nothing to us.

Unification of Rationalism and Empiricism & Synthetic A Priori PropositionsThe epistemological debate between rationalism and empiricism is basically about what extent the senses contribute to knowledge. Both rationalism and empiricism take for granted that it’s possible for us to acquire knowledge of Reality, or how things really are, as opposed to how they seem to us. But both rationalism and empiricism overlook the fact that the human mind is limited; it can experience and imagine only within certain constraints. These constraints are both synthetic and a priori. An a priori proposition is a proposition whose justification does not rely upon experience. Moreover, the proposition can be validated by experience, but is not stuck in experience. Therefore, it is logically necessary in other words the justification of these propositions does not depend on existence. A posteriori proposition is a proposition whose justification does rely upon experience. The proposition is validated by, and grounded in, experience. Therefore, it is logically contingent. Any justification of the propositions would require one's experience. All our possible experience must conform to these. Both rationalists and empiricists are wrong when they claim that we can know things in themselves. Rationalists are wrong not to trust senses but are right about innate ideas in the way that Descartes explains (we can only be sure that God exists). Kant showed that the mind, through its innate categories, constructs our experience along certain lines (space, time, causality, self, etc.). Thus, thinking and experiencing gives no access to things as they really are.