This chapter examines Aristotle's claim that the soul is an inner principle of change, against the background of his account in the Physics of nature as an inner principle of change. That for Aristotle, the study of the soul is part of the study of nature is clear already from the opening lines of the De anima, where he announces that ‘knowledge of the soul seems to contribute greatly to all truth but most of all the truth in relation to nature: for the soul is such a thing as a principle of animals’. The study of the soul is valued, then, for its contribution to our knowledge of nature. The reason for that claim is in turn that the soul is such a thing as ‘a principle of animals’. Aristotle thinks that the soul really is a principle of animals. The ‘such as’ here serves rather to put epistemic distance to the claim: we do not yet know what it means for the soul to be a principle, so the vagueness is appropriate. The chapter seeks to overcome some of that vagueness.
Keywords: nature, soul, Aristotle, De Anima, Physics, nutrition, perception