The book continues the “School of Self-Knowledge” series published by the Academy of Self-Knowledge. The first book in the series, “Introduction to Self-Knowledge,” defined a general approach to self-knowledge through purification, then the three-volume “Purification” explored the consciousness, soul and methods of their purification. In Introduction to the Science of Thinking, the author moved on to examine the workings of the mind and introduced the concepts necessary for further work. The Foundations of the Science of Thinking, in two books, is devoted to the study of how we think. The first book examines Reasoning. The research is conducted in the vein of cultural-historical psychology. For everyone interested in self-knowledge, psychology and philosophy and who wants to improve the work of their mind.