 The fundamental concepts are activity and process. … The notion of self-sufficient isolation is not exemplified in modern physics. There are no essentially self-contained activities within limited regions. … Nature is a theatre for the interrelations of activities. All things change, the activities and their interrelations. … In the place of the procession of [spatial] forms (of externally related bits of matter, modern physics) has substituted the notion of the forms of process. It has thus swept away space and matter, and has substituted the study of the internal relations within a complex state of activity. (1934 [2011: 35–36])