Bodily Prerequisites of the Mind: The Spirit as the Highest Product of Digestion

One of the various meanings that the term spiritus has assumed throughout the history of philosophy is that of a vaporous bodily substance that serves the soul. This definition binds the notion of the spirit to the notion of the body itself. The aim of this chapter is to identify the major stages of this tradition, which begins with Aristotle and Galen, who applied the notion in philosophy and medicine. During the Middle Ages, the notion was rethought, first, in Costa ben Luca’s De differentia animae et spiritus, in which the difference between soul and spirit was clarified by defining the spirit as a material principle managed by the soul. Then, Avicenna directly connected the spirit to the humours in his Canon, explaining that spirits emerge in the process of concoction. Subsequently, Albert the Great, who was strongly influenced by this tradition, defined the spirit as a vapour of radical moisture and assigned a key role to it in his description of the mechanisms of life in general and, more specifically, of the human body. Among the various powers of the soul, the spirit should serve the highest of these, pervading the inner senses, revealing a relation between the mental functions and the process of the concoction of the humours, e.g., digestion, in this tradition. This chapter analyses the steps and sources—both medical and philosophical—that led to the conception of the body as a process of becoming, involving ever more refined degrees of spirt.