Plato was a dualist, meaning that he believed that humans are composed of two elements, body and soul; two seperate entities; a corporeal body, and an ethereal soul- a view Gilbert Ryle would later attack, saying that to look for the ‘body soul distinction’ is in fact a linguistic mistake- saying that one has a body and a soul is much like claiming to be wearing a left hand glove, a right hand glove, and a pair of gloves. The ‘soul’ is simply a function of the body. Plato held that the soul was tripartite; composed of three elements in much the same way as a chariot. At the helm is the soul’s logical element, commanding the two horses- base desire, and emotional drive. When reason is in control, and coordinates the horses, life is smooth and good. When the horses are unruly, and logic is thrown aside, life becomes stressful and full of strife.
Plato held that this tripartite soul is in a constant cycle- being trapped in a human body, and then escaping the body at death to return to the ‘realm of the forms’, and back to a human body, and so on ad infinitum- as the soul is both eternal and immutable. His student Aristotle contested this viewpoint, claiming instead that soul and body were inseperable- an early materialist stance- the soul being a component of the body, helping to keep it alive and enrich it, in much the same way as blood. Descartes may have attacked Aristotle’s assertion, based on his argument from doubt- if the soul is simply a component of the body, then it’s existence can be doubted, rendering it effectively corporeal, and therefore not the metaphysical entity which Descartes believed it to be- and which, indeed, his assertion ‘Cogito Ergo Sum’ seems to prove it to be. Aristotle, however, might argue in counterpoint that a corporeal soul cannot be empirically perceived- and therefore might easily fulfill Descartes’ requirements insofar as the component which is responsible for rational thought is concerned.
Plato was fairly vague on many points concerning the moral implications of this arrangement- for instance, the problem posed by the supposed role of morality in an afterlife of immutable souls- all presumably identical. Plato asserted at some stages that indeed, maintenance of the soul is important above all things- as in ‘Charmides’- and claimed, therefore, that good souls would return to the world of forms, and dwell in closer proximity to the ‘form of the good’ than evil souls. Richard Dawkins, a biological materialist, was similarly concerned with the moral implications of his stance on body and soul- as he perceived all human life as simply complex replication, he was worried that his view could promote an amoralistic nihilism, in much the same way as Plato’s theories could. Despite this similarity, Dawkins would fiercely reject Platonic dualism, preferring instead to label ‘the soul’ as a successful ‘meme’ or unit of cultural identity. Plato might assert that existence of the soul is evident in innate knowledge, but Dawkins would counter this by claiming that all ‘innate knowledge’ can be explained by genetic happenstance.
Plato also postulated four arguments for the existence of the soul- the cyclical argument, the argument from recollection, the argument from affinity and the argument from form of life. These were- from first to last- that opposites imply each other; therefore, as the rain implies the eventual sunshine, so the sunshine implies eventual rain. In the same way, death implies life, and life death- and death must lead to a new life. The next, from recollection, uses Plato’s belief in innate knowledge- as evidenced in his ‘Meno’- to imply that innate knowledge must be present in the soul, as it could not come from the body. The third argument, from affinity, suggests that our souls are ethereal, indivisible, and immutable, whereas our corporeal bodies are perishable. The argument from form of life argues that since the number four partakes in the ‘form of the even’, and a carrot partakes in the ‘form of the vegetable’, so the soul partakes in the ‘from of life’, therefore it cannot die.
John Hick might put it to Plato that his theory of replicas implies the logical possibility of resurrection, without the need for souls. Plato, however, along with Van Inwagen, would argue that there is more to a human than simply their body- whatever it is that separates us from simple matter, a soul or otherwise, is as integral to who we are as the matter itself. This, in fact, is the crux of Plato’s theory; your soul is an integral part of you, and as it is immortal, probably your most important part. Plato’s theories promote morality and personal development- therefore, there is much value in them, however they are debated.