  Immanuel Kant (1724–1804) is the most important figure of the Enlightenment in Germany, but his project is different in many ways from those of his French contemporaries. He was brought up in a pietist Lutheran family, and his system retains many features from, for example, Crusius. But he was also indebted through Wolff to Leibniz. Moreover, he was ‘awoken from his dogmatic slumbers’ by reading Hume, though Kant is referring here to Hume's attack on causation, not his ethical theory (Prolegomena, 4:260). Kant's mature project was to limit human knowledge ‘in order to make room for faith’ (KrV, B xxx). He accepted from Hume that our knowledge is confined within the limits of possible sense experience, but he did not accept skeptical conclusions about causation or the soul. Reason is not confined, in his view, to the same limits as knowledge, and we are rationally required to hold beliefs about things as they are in themselves, not merely things as they appear to us. In particular, we are required to believe in God, freedom and immortality. These are three ‘postulates of practical reason’, required to make rational sense of the fact of moral obligation, the fact that we are under the moral law (the ‘categorical imperative’) that requires us to will the maxim of an action (the prescription of the action together with the reason for it) as a universal law (removing any self-preference) and to treat humanity in any person as always at the same time an end and never merely as a means (Groundwork, 4.421, 429). Kant thought that humans have to be able to believe that morality in this demanding form is consistent in the long run with happiness (both their own and that of the people they affect by their actions), if they are going to be able to persevere in the moral life without rational instability. He did not accept the three traditional theoretical arguments for the existence of God (though he was sympathetic to a modest version of the teleological argument). But the practical argument was decisive for him, though he held that it was possible to be morally good without being a theist, despite such a position being rationally unstable.