In adopting a system perspective on language, systemic functional linguistics have been part of a more general 20th- and 21st-century reaction against atomistic approaches to science, in which an essence is sought within smaller and smaller components of the phenomenon under study. In systems thinking, any delineated object of study is defined by its relations to other units postulated by the theory. In systemic functional linguistics, this has been described as the trinocular perspective. Thus a descriptive category must be defended from three perspectives: from above ("what does it construe?" "what effect does it have in a context of use?"), below ("how is this function realised?") and round about ("what else is in the neighbourhood?" "what other things does this thing have to interact with?"). This gives systemic functional linguistics an affinity with studies of complex systems.