Aristotle's [[psychology]], given in his treatise [[On the Soul]] (''peri psyche'', often known by its [[Latin]] title ''De Anima''), posits three kinds of [[soul]] ("psyches"): the vegetative soul, the sensitive soul, and the rational soul. Humans have a rational soul. This kind of soul is capable of the same powers as the other kinds: Like the vegetative soul it can grow and nourish itself; like the sensitive soul it can experience sensations and move locally. The unique part of the human, rational soul is its ability to receive forms of other things and compare them.
For Aristotle, the soul (''psyche'') was a simpler concept than it is for us today. By soul he simply meant the [[Hylomorphism#Body-soul hylomorphism|form]] of a living being. Since all beings are composites of form and matter, the form of living beings is that which endows them with what is specific to living beings, e.g. the ability to initiate movement (or in the case of plants, growth and chemical transformations, which Aristotle considers types of movement).<ref>Stanford Encyclopedia of Philosophy, article [http://plato.stanford.edu/entries/aristotle-psychology/ "Psychology"].</ref>