We all know that Kant held ethics and empirical science to be separate, incommensurable disciplines. He also claimed that his views about ethical and empirical knowledge fit together in a single "Critical" system. In the essay that follows I want to sketch a modern, 'semantic," interpretation of Kant's philosophy which explains both the unity of the critical system and the unbridgeable gap between ethical and empirical knowledge. I believe that this interpretation can help resolve some exegetical problems that appear to plague Kant's theories about ethics and empirical science. And I believe that it can also focus attention in a new way on some aspects of Kant's moral theory that seem most troubling today.