The term or spiritus has a long history in Western natural philosophy. Its extensive use and elaboration in the Graeco-Roman world formed the background for medieval and Renaissance treatments. Although the Stoic and Neoplatonic traditions, as well as such authors as Vergil, Macrobius, Nemesius, and Augustine, are important, the present article will attempt only to survey some medieval understandings of the Aristotelian and Galenic spiritus, which provided the basis for medicine and biological speculation.
The earliest moments of medieval Latin theoretical medicine are marked by the assimilation of Greek medicine and natural philosophy from the living tradition of Arabic medicine and philosophy. With respect to spiritus, Arabic modifications which mediated the assimilation of Aristotle's and Galen's views led to a multiplicity of meanings being attached to the term spiritus, especially where the ancient resources were applied to problems generated by the mingling of diverse cultural and religious systems. A second result was the attempt to fix, through critical interpretation, the specific medical meaning attributable to the term spiritus, to define the domain of animate beings to which spiritus belonged, and to justify philosophically and theologically the quite restricted nature of the term spiritus. If the former tendency was the legacy of the broader and more fluid concerns of the twelfth century, the latter, we shall see, was the standpoint bequeathed to later medieval and Renaissance medicine by authors like Albertus Magnus.