Psychometrics is not measurement unraveling a fundamental misconception in quantitative psychology and the complex network of its underlying fallacies.

Psychometrics has always been confronted with fundamental criticism, highlighting serious insufficiencies and fallacies. Many fallacies persist, however, because each critic explores only some fallacies while still building on others. This article scrutinizes the epistemological, metatheoretical, and methodological foundations of psychometrics, revealing a complex network of numerous conceptual fallacies underlying its framework of theory and practice. At its core lies a key challenge for psychology: the necessity to distinguish the phenomena under study from the means used to explore them (e.g., concepts, methods, data). This distinction is intricate because concepts constitute psychical phenomena in themselves and many psychical phenomena are accessible only through language-based methods. The analyses show how insufficient consideration of this important distinction and common misconceptions about concepts and language (e.g., signifier–referent conflation, reification of constructs) led to conflations of disparate notions of key terms in psychological measurement (e.g., “variables”, “attributes”, “causality”) and numerous interrelated fallacies (e.g., construct–referent conflation, phenomenon–quality–quantity conflation, numeral–number conflation). These fallacies are maintained and masked by repeated conceptual back-and-forth switching between two incompatible epistemological frameworks, (a) an operationist framework of data modeling implemented through methodical and statistical operations and (b) a realist framework of measurement sporadically invoked in theoretical considerations but neither theoretically elaborated nor empirically implemented. The analyses demonstrate that psychometrics constitutes only data modeling but not data generation or even measurement as often assumed and that analogies to (indirect or fundamental) physical measurement are mistaken. They provide theoretical support for the increasing criticism of psychometrics and its use in research and applied contexts.