If, as we saw in the last chapter, Kant's Critique of the Power of Judgment (1790) showed some possible escape routes from the critical system, routes which the German Idealists later explored, the Opus Postumum (1804) is a work that appears to simultaneously break with, and yet shore up, the speculative reach of the critical project. While one could engage The Metaphysical Foundations of Natural Science (1786) as Kant's definitive and sophisticated engagement with the physical sciences, fully determining the relation of inner and outer sense, I will address the far more controversial Opus Postumum for several reasons. Centrally, the Opus Postumum is Kant at his seemingly least critical and most metaphysical, following the muchvaunted Copernican turn. Kant's Copernican turn, as has been widely discussed, placed the subject-as-observer at the centre of the epistemological cosmos. In other words, for Kant, the forces and dynamics detected in outer sense are made possible by the forms of inner sense in order for us to speak about the world at all. Whether this placement is a necessary assumption for a modest epistemological stance, or whether it amounts to a form of anthropocentrism in thinking, remains a much-debated issue. Confusion over the nature of Kant's revolution, I argue, stems largely from collapsing a position (where we know from) and subject–object relation (what has the final say on the judgement of the knower on the known, or the known's eff ects on the knower). While Schelling would be critical of Kant on the later point, he would fully appreciate the uprooting of humanity's fixed place in the cosmos coextensively actual and epistemological.

In the Opus, Kant touches upon Schelling's work (albeit slightly) and, more extensively, engages with numerous Schellingian themes close to our project here: the importance of motion, the continuity of nature and the division between speculative metaphysics and empirical physics. More specifically, while in the Critique of Pure Reason Kant moved away from absolutising space to relying on an internal and ideal space of observation, he appears to swing back towards something more like absolute space in the Opus.