 Kant’s argument is bold but dubious. He holds that we must think of moral activity as really resulting in happiness. Yet human agency is nowhere near adequate to this task: “I [or indeed we] cannot hope to produce this [highest good] except by the harmony of my will with that of a holy and beneficent author of the world” (5:129). So, Kant argues, we must postulate God’s existence. We must also postulate immortality, since this enables us to hope that we will come closer to virtue so as to be worthy of happiness. (Reath 1988 argues that Kant sometimes also deploys a more defensible, “secular” or this-worldly, notion of the highest good. Further recent discussion includes Kleingeld 1995 and Guyer 2000a &amp; 2000b.)