  William's treatise On the Soul is one of the most substantial Latin works on the topic from before the middle of the thirteenth century. Although William begins this treatise with Aristotle's definition of the soul as the perfection of an organic body potentially having life, his conception of the soul is heavily influenced by Avicenna and decidedly Platonic in character. He interprets Aristotle's definition to mean that the body is an instrument of the soul (as he thinks the term “organic” indicates) and that “a body potentially having life” must refer to a corpse, since a body prior to death actually has life.  And although he calls a soul, with Aristotle, a form, unlike Aristotle he holds that a soul is in fact a substance, something individual, singular and a “this something” (hoc aliquid), not at all dependent on the body for its existence.