A distinctive feature of modern European culture, and in of modern science, in particular, is an all-encompassing trend towards rationalization. Rooted in the philosophical revelations of Descartes, the scientific discoveries of Galileo and Newton and fully embodied in the age of Enlightenment, the rationalizing trend of modern European culture originates in the belief of the absolute value of reason. Scientists of the past and modern researchers have repeatedly problematized the rationalizing tendency of modernity, pointing to the tendency of reason in the absence of authority to go beyond its own boundaries. The consequences of this violation of boundaries, embodied in the establishment of a strict and unifying order, as history demonstrates, create tyranny and authoritarian societies. This fact raises the question of preserving and addressing the irrational in culture. The irrational, present both in the individual and in the social strata of culture, in history, from the perspective of modern European culture, was most clearly manifested in alchemy. The article deals with the initial principles and metaphysical foundations of the alchemical tradition, which historically preceded modern science and, in many respects, served as the basis for its emergence. In contrast to the mechanistic and mathematical approaches to the description of physical phenomena characteristic of modern science, alchemy used the language of symbols, and operated with the data of imagination and imagination. The article problematizes the irrationality of the alchemical tradition, which upon closer study reveals a consistent, original and holistic worldview and logic. Alchemical knowledge is based on the relationship of physical and mental, macrocosm and microcosm, divine participation in alchemical practices. According to J. von Liebig, D. I. Mendeleev and other classics of chemical science, alchemy has prepared an extensive body of empirical data, without which the new European chemical science would not have the material for theorizing. However, the claim that modern science, and chemistry, in particular, rationalized alchemy does not adequately reflect the relationship of the two cognitive traditions. Alchemy and modern European science are fundamentally different in their goals, methods and ideological attitudes. The influence of alchemy continued into modern times. Alchemy not only contributed to the emergence of new European science, but also served as a source of ideas for C. G. Jung in his study of active imagination, and also expanded the understanding of the further development of quantum physics for W. Pauli.