The individual system as a central object of research in psychology and its links to theories of social psychology

The crisis in psychology stems from the lack of a clear definition of its subject matter (Witte, 2025). There has always been a contradiction between person-centered and average-centered perspectives. This contradiction can be overcome by defining the object of psychological investigation as an individual system. The feasibility of this approach can be examined by linking it to existing theories. To this end, the second volume of the Handbook of Theories of Social Psychology is consulted, and 24 theories are linked to the basic model of the individual system. Aristotle's three causes (material, efficient, and final) are used as a structure for the relationship to answer three questions through theories: The WHAT question, the HOW question, and the WHY question, according to the three causes. Aristotle's fourth cause (causa formalis) is a higher-level consideration and is excluded at this level of analysis. The following approaches are considered as theories: Self-control theory; self-verification theory; implicit theories; uncertainty-identity theory; optimal distinctiveness theory; a cognitive-neoassociation theory of aggression; attachment theory; shared reality theory; equity theory in close relationships; the investment model of commitment processes; a theory of communal (and exchange) relationships; interdependence theory; Theories of cooperation-competition and beyond; normative conduct; system justification; justice; minority influence; social identity; self-categorization; social dominance; the common ingroup identity model; social role; social representation; and individualism-collectivism are also considered. None of these theories can provide answers to "why" questions in the strictest sense. However, minor but convincing additions to the formulation of the processes of the object of investigation can be used to expand it as an individual system model. All theories can be easily linked to the research object.