Aristotle—Greek philosopher who taught in the fourth century before Christ (384-322 BC). Aristotle studied under Plato for almost twenty years, then went on to start his own school of thought. He was very interested in what the Bhagavad-gītā calls the field of knowledge, which he analyzed minutely according to his own system. He was less concerned with the knower of the field, the soul. He defined the soul as What it is to be for a body of the character just assigned (De anima, 412b). In other words, if an axe was a product of nature, then its characteristic body or form would be its soul. (The ax example is Aristotle's own.)