The term soul is horribly overused, even, or perhaps especially, by advocates of the philosophy in which it belongs. Soul is just a species of act as opposed to potency, form as opposed to matter. Speaking very loosely, therefore, all actual existents have a ‘soul’, since on Aristotelianism, existence is the dynamic union of form and matter. (I’m bracketing abstract and truly supernatural modes of being, of course.)To speak more precisely, soul properly refers to the act of living as opposed to nonliving (“in-anima-te”) organisms.
The ‘lower’ a thing is ontologically, the closer it is to the potency of matter; the closer it is pure potency, the more amenable or susceptible it is to being ‘reduced’ by a higher formal agent. Hence the soul––or formal unity–– of a plant is ‘overtaken’ (or ‘deanimated’) by the soul––or formal unity–– of a rabbit, which is in turn overtaken by that of a hunter at dinner. On their own, microbes have their own proper teleology, yes, but it’s a very weak kind of teleology, which is why, like embers always susceptible to extinction, they ‘tend to’ function in groups. As Gilson remarks in From , cells don’t exist independently, but as tissue of an organism. Down the ontological ladder, the same holds for atoms: they only exist as the elements of some formally more-integrated substance. Hence, in a metaphysically imprecise way of speaking, microbial finality is ‘subjugated by’ or ‘defers to’ the finality of the larger organism, just as neurons function best as the cells of a cerebral organism. to Darwin