Causal refutations of idealism

In the 'Refutation of Idealism' chapter of the first Critique, Kant argues that the conditions required for having certain kinds of mental episodes are sufficient to guarantee that there are 'objects in space' outside us. A perennially influential way of reading this compressed argument is as a kind of causal inference: in order for us to make justified judgements about the order of our inner states, those states must be caused by the successive states of objects in space outside us. Here I consider the best recent versions of this reading, and argue that each suffers from apparently fatal flaws.