 Twardowski was a sharp thinker and a writer of exemplary clarity. He wrote on signs, on meaning and reference, and on indexicality and truth, defending a non-platonistic view of time-independent truth; he wrote on the metaphysics of parts and wholes, on ethics, on the history of philosophy, on the relation between philosophy and psychology, and, importantly, on metaphilosophy. In Twardowski's times psychology was divided roughly in two camps: ‘Wundtian’ experimental psychology and ‘Brentanian’ descriptive pyschology (see the entries on  Wundt  and  Brentano);  although Twardowski sided mainly with Brentano's way of looking at psychology, he lectured on themes from experimental psychology such as optical illusion and established the first laboratory of empirical psychology in Poland. He developed a judgment-based theory of knowledge, and he valued analysis as a fruitful method in philosophy. This notwithstanding, it is a widespread convinction that Twardowski's most tangible success remains his extraordinary work as educator and initiator of philosophical activities in Poland. Indeed, Twardowski was a talented teacher, like Brentano, and he exerted, through his teaching, a powerful influence on generations of young Polish philosophers, such as Jan Łukasiewicz, Kazimierz Ajdukiewicz, Stanisław Leśniewski (who, in turn, taught Alfred Tarski) and Tadeusz Kotarbiński. This influence regarded first of all matters of method: Twardowski laid emphasis on ‘small philosophy’, namely on the detailed, systematic analysis of specific problems—including problems from the history of philosophy—characterised by rigor and clarity, rather than on the edification of whole philosophical systems and comprehensive world-views.