In his three Critiques: the Critique of Pure Reason (1781, 1787), the Critique of Practical Reason (1788), and the Critique of the Power of Judgment (1790), Immanuel Kant argues that human autonomy is the foundation of all understanding.
Kant strove to resolve the oppositions of the approaches of empiricism and rationalism by the pure processes of reason. For, Kant contended that empiricism, which holds that knowledge arrives from experience, and rationalism, which holds that innate ideas precede experience and is attained independently of sensual experience, are unified by the rational mind's role in both. That is, the human mind is "the final end of nature."
In his Critique of Pure Reason, Kant argues,
... all our intuition is nothing but the representation of appearance; that the things that we intuit [with the rational mind] are not in themselves what we intuit them to be, nor are their relations so constituted in themselves as they appear to us; and that if we remove our own subject or even only the subjective constitution of the senses in general, then all constitution, all relations of objects in space and time, indeed space and time themselves would disappear, and as appearances they cannot exist in themselves, but only in us.
Certainly, one essential result of this philosophy is that a person never has direct experience with the world as it is always evaluated through the rational process. Without a truly direct experience of the world, then, it is possible that what man perceives through his senses and rational mind may, indeed, not exist outside of "the subjective constitution of the senses." For this reason, then, the world per se does not play an intrinsic role in Kant's philosophy. This contention of Kant's that humans experience only appearances of something, rather than the actual thing, and that time and space are merely subjective forms of human intuition and may not really exist is his most controversial thought. It is known as Transcendental Idealism. Nevertheless, Kant does argue that one must distinguish the objective unity of given representations from the subjective. For example, all people would perceive the size and shape of man's childhood home, but he may have subjective feelings of such things as security or nostalgia that could enter into his perception.