Common sense or common sensation – sensus communis in Latin – was an innovation of Aristotle (De anima, 3.1) adopted by ancient physicians as they assigned physiological locations to psychological powers. Aristotle differentiated the proper sensibles (sense qualities, like color in vision or tone in hearing, that are specific to a single sense) from common sensibles like unity/number, magnitude, shape, motion, and duration, which appear to more than one sense. Common sensation unites proper and common sensibles in the fully articulated sensory field of ordinary experience. Aristotle located this function near the heart, but later Aristotelians quickly adjusted to the consensus of physicians, who placed it in the brain. It was temporally and logically the first of the inner (inward, internal) senses. These included memory, imagination, the animal ability to quickly “estimate” whether what presented in sense appearances was noxious or good, and even the human capacity to name forms presented in sensation.
Having the authority of both Aristotle and physicians, this general schema was almost universally accepted by thinkers and natural philosophers well into the early modern period. It was the psychophysiological basis of Islamic and Western medieval theories that understood cognition as requiring the abstraction of intelligible forms from sense experience. Common sensation receives and unites sensible images of things, called “phantasms.” Higher animals can retain, reproduce, and process these phantasms by means of memory, imagination, and estimation. In human beings, this work of the inner senses “prepares” phantasms for the final step, in which active intellect illuminates the phantasms and thereby abstracts from them an intelligible species, which is impressed and preserved in potential (passive, receptive) intellect and produces cognition (see species, intentional).
Medieval theorists often increased the number of these basic powers by distinguishing and subdividing their functions. Following the existing medical conceptions about brain location, they distributed them to different locales in the ventricles (the hollows at the base of the brain produced by the anatomical enfolding of the left and right cerebral hemispheres). Sixteenth- and seventeenth-century psychophysiology simplified this scheme by reducing the number of psychological powers to common sensation, imagination, and memory.
Descartes began with this tradition and eventually arrived at his theory of the pineal gland as the focus of nerve and animal-spirit functions. Like many physicians, he assigned the psychological powers to organs in the brain rather than to the hollows preferred by late Scholastic philosophers (see animal spirits). A first step occurs in Rule 12 of the Rules for the Direction of the Mind.