What Aristotle meant by soul, he meant the moving principle of life. And there's nothing vitalist about it, there is nothing metaphysical about it. It's hard to get a grip on what he meant, but it's a resolutely empirical kind of concept. What he meant was something like this, he says all living things have a soul, and when they die, the soul disappears. So none of that nonsense about the immortality of the soul. Plato thought souls were immortal, many people, popular belief had that the souls were immortal, but Aristotle is clearly using soul in a very special, and technical, and new sense. It's the moving principle of life.
