The Critique of Pure Reason is the most important work of philosophy written in modern times. ‘The background of Kant's thought’ presents, with as few technicalities as possible, an explanation of what Kant was trying to achieve in this work. The first question to ask is: what are the questions that Kant hoped to answer? The most important problem that confronted him was the notion of objective knowledge. Kant's aim was firstly to show that synthetic a priori knowledge is possible, and to offer examples; and secondly, it was to demonstrate that ‘pure reason’ alone, operating outside the constraints placed on it by experience, leads only to illusion, so that there is no a priori knowledge of ‘things-in-themselves’.