Kant's philosophy of religion has perplexed even his warmest admirers. Nobody has pointed this out more amusingly than Heinrich Heine, who saw in Kant the Robespierre of the intellect. The orderly philosopher of Königsberg, whose daily constitutional was attended and sheltered by his servant Lampe, armed with a modest umbrella, was really a terrorist who destroyed the ancien régime of European religion and philosophy. The Critique of Pure Reason was the sword that killed deism in Germany. Yet Kant, Heine suggests, derailed this sublime and terrifying philosophy, that pointed towards the death of God, when a domestic difficulty arose. He relented and patched a God together because his servant, old Lampe, was disconsolate. Heine lampoons Kant:

If Heine and other critics are right, Kant's retreat is ignominious. In the First Critique he asserts the death of God: ‘No one indeed will be able to boast that he knows that there is a God and a future life’ (CPR A 828–9 / B 856–7); in the Second Critique he argues for God and immortality. Can practical reason really produce a magic wand to revive the corpse of deism – let alone a more comfortable religion for old Lampe? Or does it provide no more than an old man's umbrella as defence against the terrifying weapons of theoretical reason?