Kotarbigski Tadeusz (1886–1981), Polish philosopher, cofounder, with Lukasiewicz and Lesniewski, of the Warsaw Center of Logical Research. His broad philosophical interests and humanistic concerns, probity, scholarship, and clarity in argument, consequent persuasiveness, and steadfast championship of human rights made him heir to their common mentor Kasimir Twardowski, father of modern Polish philosophy. In philosophical, historical, and methodological works like his influential Elements of Theory of Knowledge, Formal Logic, and Scientific Methodology (1929; mistitled Gnosiology in English translation), he popularized the more technical contributions of his colleagues, and carried on Twardowski’s objectivist and ‘anti-irrationalist’ critical tradition, insisting on accuracy and clarity, holding that philosophy has no distinctive method beyond the logical and analytical methods of the empirical and deductive sciences. As a free-thinking liberal humanist socialist, resolved to be ‘a true compass, not a weathervane,’ he defended autonomous ethics against authoritarianism, left or right. His lifelong concern with community and social practice led him to develop praxiology as a theory of efficacious action. Following Lesniewsi’s ‘refutation’ of Twardowski’s Platonism, Kotarbigski insisted on translating abstractions into more concrete terms. The principal tenets of his ‘reist, radical realist, and imitationist’ rejection of Platonism, phenomenalism, and introspectionism are (1) pansomatism or ontological reism as modernized monistic materialism: whatever is anything at all (even a soul) is a body – i.e., a concrete individual object, resistant and spatiotemporally extended, enduring at least a while; (2) consequent radical realism: no object is a ‘property,’ ‘relation,’ ‘event,’ ‘fact,’ or ‘abstract entity’ of any other kind, nor ‘sense-datum,’ ‘phenomenon,’ or essentially ‘private mental act’ or ‘fact’ accessible only to ‘introspection’; (3) concretism or semantic reism and imitationism as a concomitant ‘nominalist’ program – thus, abstract terms that, hypostatized, might appear to name ‘abstract entities’ are pseudo-names or onomatoids to be eliminated by philosophical analysis and elucidatory paraphrase. Hypostatizations that might appear to imply existence of such Platonic universals are translatable into equivalent generalizations characterizing only bodies. Psychological propositions are likewise reducible, ultimately to the basic form: Individual So-and-so experiences thus; Such-and-such is so. Only as thus reduced can such potentially misleading expressions be rightly understood and judged true or false. See also POLISH LOGIC. E.C.L.