Understanding can yield objective knowledge, but it also contains a temptation to illusion. Kant tries to diagnose and criticize this temptation in his examination of ‘pure reason’. ‘The logic of illusion’ examines the idea of illusion and looks at the subjective and objective sides that form Kant's analysis. Kant describes reason in its illegitimate use and refutes claims to knowledge that this faculty tempts us to make. He divides rationalist metaphysics into three categories: rational psychology, concerning the nature of the soul; cosmology, concerning the nature of the universe and our status within it; and theology, concerning the existence of God. Each, he states, proceeds in accordance with its own version of illusory argument which leads towards fallacy.