The ontological turn in Castoriadis' thought is exemplified in The Imaginary Institution of Society (IIS). Castoriadis did not stop there, however, but was drawn to enquire into more general ontological questions. In turn, this line of questioning made its presence felt significantly in Castoriadis' intellectual trajectory, such that, as I argue in this article, we can speak of a shift from a regional ontology of the social-historical (as developed in the IIS) to a later transregional ontology of physis as creative (...) emergence. Castoriadis' ontology of physis occurs at the convergence of three intertwined threads in his thought: the rethinking of the idea - and regions - of nature, his growing onto-epistemic critique of `objective' knowledge and his theorization of the creativity of being via time. This leads him to develop an (unfinished) philosophical cosmology that, although placing more emphasis on continuity between anthropic and non-anthropic modes of being, can still highlight the autonomy and uniqueness of the social-historical. (shrink)