Immanuel Kant's Critique of Pure Reason, first published in 1781, is generally considered to be one of the most important and one of the most difficult texts in the history of philosophy. In it, Kant develops his theory of transcendental idealism, which aims to provide a corrective to the problems generated by the theories offered by both his rationalist and his empiricist predecessors. The Critique of Pure Reason is thus where Kant lays out his own theory of knowledge (his “transcendental epistemology”) and where he “critiques” metaphysics.

That reason needs a “critique” is demonstrated, according to Kant, by the fact that neither the empiricist nor the rationalist approaches had succeeded in resolving fundamental issues in epistemology and metaphysics. The methodological approach of the empiricists had, in the hands of Hume, only led to a form of pernicious scepticism, a scepticism that threatened to undermine empirical knowledge and science. That of the rationalists had opened up the floodgates for an unrestrained dogmatism, a dogmatism that flourished in the transcendent metaphysical theories about the soul, the world and God.

The problem of synthetic a priori knowledge

Kant's theoretical philosophy is often viewed as a response to a fundamental question: how are synthetic a priori propositions possible? Justifying such principles is important to Kant because he believes that many of our judgements about the world are of this type; knowledge of nature is based on principles that state more than what can be known through logic alone, and yet such principles cannot be justified by any particular experience.