Knowledge of the Essence of the Soul

It was a commonplace in medieval philosophy that no one can be in doubt about the existence of one’s own soul. For example, Matthew of Aquasparta refers to Augustine’s The City of God (XI, 26) as having given the final refutation of the radical skeptical position by pointing out the certain knowledge of one’s own existence. There was, however, a widespread opinion about exactly how such selfknowledge is grounded and what it contains. Can one have direct self-consciousness in the sense of experiencing oneself as a mental subject, or is such knowledge mediated through experiences of mental acts so that the subject of the acts is not as such a possible object of consciousness? If the soul itself can be experienced, does this experience yield knowledge of the incorporeality of the soul or its separability from the body?

Before Aristotelian thought gained importance in the thirteenth-century universities, Latin authors followed the Neoplatonic tradition and affirmed that it is possible to turn intellectually inward to one’s mental self. According to an Augustinian argument that was often quoted in the Latin Middle Ages, the soul’s incorporeality can be directly grasped in the immediate awareness of oneself that is unlike any awareness of anything corporeal. Also, Avicenna’s ‘‘floating man’’ thought experiment was well known among the Latin thinkers. In this thought experiment, one is to imagine oneself as being created as if floating in air without any sensory experiences. As Avicenna claims, the thought experiment shows how one can know one’s own existence without any knowledge of the body, and that therefore one should conceive of oneself as an incorporeal soul. Franciscan thinkers developed the epistemological aspects of this Augustinian-Avicennian understanding of the structure of self-consciousness.

Aristotelian thinkers like Thomas Aquinas claimed that the essence of the soul cannot be directly experienced, and even knowledge of the existence of one’s own soul comes through experiencing the acts of the soul. Knowledge of the incorporeality of the soul comes through scientific study rather than direct experience. Some other thinkers followed Averroes’ interpretation of the Aristotelian position, which implied an even stronger denial of direct self-consciousness.