 In the aftermath of organicism, development of the levels concept splintered into different intellectual trajectories, with little overall theoretical or conceptual coherence. One direction of development flowed through the framework of general systems theory (von Bertalanffy 1950, 1968), and particularly through so-called hierarchy theory (Whyte et al. 1969; Weiss 1971; Pattee 1973). General systems theory sought to construct isomorphisms between laws of different scientific fields based on their generic system properties (von Bertalanffy 1950: 136), but nonetheless continued to emphasize the hierarchical structure of systems (von Bertalanffy 1968). ‘Levels of organization’ in this tradition was ultimately given secondary consideration to the articulation of system-generic properties and laws. Similarly, in hierarchy theory, ‘levels’ tend to be treated as derivative of the more general notion of a hierarchy, or the ordering of a system into nested subsystems (Simon 1962 [1996: 184–5]; see also Weiss 1971). Hierarchy and levels alike continued to be treated as generic structures of systems of all stripes (see also Allen &amp; Starr 1982; O’Neill et al. 1986). However, one important distinction to come out of this tradition was the distinction between levels of composition and levels of control (Simon 1962; Pattee 1973). The former speaks to the nested compositionality typically identified with levels of organization, while the latter refers to the idea that higher levels impose constraints on the processes at lower levels, for example by limiting the degrees of freedom of the system at a lower level (Pattee 1973: 85).