  So far Kant has ‘deduced’ only three of the four kinds of categorical concepts, number, quality, and modality. He has said nothing about the relational categories. For Kant, this would have been a crucial gap. One of his keenest overall objectives in CPR is to show that physics is a real science. To do this, he thinks that he needs to show that we must use the concept of causality in experience. Thus, causality is likely the category that he cared more about than all the other categories put together. Yet up to A106, Kant has said nothing about the relational categories in general or causality in particular. By A111, however, Kant is talking about the use of the relational categories and by A112 causality is front and centre. So it is natural to suppose that, in Kant’s view at least, the material between A106 and A111 contains an argument for the necessity of applying the relational categories, even though he never says so.