For the first time, the main works of the famous Polish philosopher Kazimierz Twardowski, who is considered the founder of the Lviv-Warsaw School and a representative of the early stage of the development of analytical philosophy (scientific philosophy), were translated into Ukrainian. The book presents the views of Casimir Twardowski on epistemology, ethics and aesthetics, psychology and logic. After reading this book, the reader will get a holistic picture of the intellectual work of Casimir Twardowski, understand the origins of analytical philosophy and the peculiarities of its methods of solving philosophical problems. The book is addressed to all who are interested in the history of Western philosophy, in particular its direction, such as analytical philosophy.