What is Aristotle’s conception of the soul?
Aristotle considers the soul to be the principle of life, which means that he holds that all living things have souls, not just human beings. His main work on psychology is called “De Anima,” which translates to “On the Soul.”
A key concept in Aristotle’s corpus is the idea of hylomorphism, which is the idea that things are composed of two principle parts: matter and form. In the case of a chair, the matter would be the wood from which it is made, and the form would be its function, or “chair-ness,” i.e. four posts and a flat surface for sitting. (Yes, there are other forms for chairs.) The key point of the “form” of “chair-ness” is that whatever physical shape it takes, the purpose or end (Greek telos) of a chair is that it be sat upon. So with this framework in mind, Aristotle claims that the soul is the form of the body (the body being the material part, or matter).
So the soul is, for Aristotle, the animating principle of living beings. When a living being dies, it is the separation of the soul (or principle of animation or motion) from the body (matter, or physicality). The body remains, but it doesn’t move anymore. Aristotle feels the question that philosophers are often so interested in, “Are the body and soul one, or two separate things?” is kind of irrelevant. He claims that if we aren’t going to ask whether the wax a candle is made of and the shape and function that it has are the same, there’s no real reason to ask such a question about the human body and soul.
I've included some helpful links. eNotes has a summary of De Anima, and there is a link to the Project Gutenberg full text of the work, plus Stanford Encyclopedia of Philosophy's entry on Aristotle's psychology (this resource is fairly advanced, but explains things well and in-depth). Hope this helps!