 Kazimierz Twardowski (1866–1938) was an Austrian-born Polish philosopher. He was a student of  Franz Brentano  and the founder of the  Lvov-Warsaw School.  His main work, On the Content and Object of Presentations (1894), established the need for the distinction between the content and the object of a presentation within Brentanian theories of the intentionality of mental acts. The distinction is a psychological, non-platonistic counterpart of Frege's distinction between sense and reference. Other students of Brentano, notably Edmund Husserl and Alexius Meinong, integrated the distinction between content and object in their works after the appearance of Twardowski's book. Twardowski spoke of contradictory objects before Meinong: he was the first philosopher to hold a theory of intentionality, truth, and predication in which thinking and speaking about non-existents, including contradictions, involves presenting and naming non-existents, including contradictory objects. Like Meinong, Twardowski belonged to a tradition of non-idealistic German-language philosophy that originated with Bernard Bolzano, and that influenced, via G. F. Stout, Moore and Russell's transition from idealism to analytic philosophy. After moving to Lvov (now Lviv) in 1895, Twardowski devoted himself to establishing a tradition of scientific, i.e. rigorous and exact philosophy in Poland inspired by Brentano's views rather than to publishing his own ideas. As a result, his published oeuvre, written in Polish and German, is relatively small. Twardowski's unpublished manuscripts, often complete sets of lecture notes, constitute a considerable part of his philosophical corpus. According to Roman Ingarden, assessments of Twardowski's achievements and his role in history should be considered incomplete and hypothetical as long as they are based only on his published writings (Ingarden 1948, 18). Important projects for the edition and dissemination of Twardowski's manuscript material have been recently completed or are currently ongoing in Austria, France, Poland, Italy, and the  Netherlands.[1]