 There is also a tension in Diderot’s approach to determinism between his acceptance of physicalism (“there is only one kind of cause … physical causes”: to Landois, DPV IX: 258) and causal closure (“the physical world and the moral world are one and the same”: PC; DPV XX: 53), and his insistence that agency, which for him covers the action of complex organisms overall and is not restricted to humans or even higher mammals, requires another, specific kind of causality: “I am a man, and I require causes proper to man” (RH; DPV XXIV: 523). Diderot is not defending free will or an unchallenged space of agency, yet there is a kind of residual anthropocentrism in some of his arguments, presented in the language of unified causality. As he explains: