The book is based on the distinction between two types of knowledge: descriptions and prescriptions. The main thesis of the book: the descriptions are true, the prescriptions are rational. The main provisions of the classical theory of truth, the theory of conformity. The difficulties that led to its modern crisis and attempts to replace it with non-classical theories are analyzed. Suggested means of overcoming these difficulties, stemming from the initial principles of the theory of conformity. Rationality of prescriptions is interpreted in the book as their compliance with the laws of nature, the needs of people and historically conditioned means of their satisfaction. The relationship of the problem of rationality with the problem of values and the problem of causa finalis of human history is analyzed For students of philosophy and teachers of philosophy .