This chapter argues, provocatively, that among all those who proposed a new ontology during the general revival of ontology at the start of the twentieth century, Hartmann was the only thinker to have actually developed one, and one that may fulfill the promise of an ontology of nature. Hartmann's critical ontology effectively challenges anthropocentrism because his conception of a stratified reality acknowledges the asymmetrical dependence of humans on nonhuman biotic and abiotic nature. Given that, for Hartmann, class="EmphasisTypeItalic ">all relations (organic, psychological, material, cultural, etc.) count, his ontology can form the non-reductive basis for a critical environmental philosophy.