Behaviourism and the meaning of mental terms the critical realists have been unable to shed the thrall of scientific behaviourism and the behaviouristically oriented philosophy of ordinary language usage. Earlier formulations of the view were mainly concerned to give a physicalist account of those residual 'mental' phenomena that resisted behaviourist analysis. Mind–brain identity theory is central to the physicalist view in its contemporary form. The various versions of identity theory (IT) all employ these distinctions more or less explicitly to fulfil Leibnitz's criterion of identity, so that the theory may be summarily represented as follows. The distinctions drawn between different 'isms' are instructive but should not be taken to indicate any fundamental disagreement about the basic physicalist–objective model rather there is a difference in emphasis only. Although the foregoing summary outlines the essentials of an IT, it has become something of a convention to distinguish three significant variants. These might be called 'Raw-Feelist', 'Critical Realist' and 'Eliminationist' views.