The book is designed to introduce the reader to the world of the basic principles and operations of human thinking. It provides an accessible, clear and at the same time quite strict and systematic presentation of modern ideas about the activity of thinking. The book will help deepen spontaneously formed logical intuition and develop the skills of consistent and demonstrative reasoning. Finally, there are some fun, although some thought-provoking, logic problems. The publication is intended for a wide range of readers.