Aristotle's Idea of the Soul considers the nature of the soul within Aristotle's psychology and natural philosophy. A survey is provided of the contemporary interpretations of Aristotle's idea of the soul, which are prominent in the Aristotelian scholarship within the analytic tradition. These interpretations are divided into two positions: `attributivism', which considers the soul to be a property; and `substantialism', which considers it to be a thing. Taxonomies are developed for attributivism and substantialism, and the cases for each of them are considered. It is concluded that neither position may be maintained without compromise, since Aristotle ascribes to the soul features that belong exclusively to a thing and exclusively to a property. Aristotle treats the soul as a `property-thing', as a cross between a thing and a property. It is argued that Aristotle comes by this idea of the soul because his hylomorphism casts the soul as a property and his causal doctrine presents it as a causal agent and thereby as a thing.