Plato believed that the soul, if it were to be the animator of all living things, must be responsible for a person's mental or psychological activities and responses. For the soul cannot be the reason for life, yet at the same time limited in its influence over the bodies in which it animates. However this provides one of the most serious and potentially defeating criticisms of Plato’s views on the soul. He fails to address the issue of the interrelationship between body and soul, if they are indeed distinct. Does the soul act as controller of a lifeless body, or is there more to the body than simply the material. Moreover the argument from affiliation would suggest that the body is concerned with the material, composite world whilst the soul is concerned with the invisible and simple world. If this is the case then the soul cannot, following from Plato’s argument, have any interaction with the material, bodily world; for then it ceases to be simple and immutable.
An argument from recollection, which Plato first put forward when discussing his theory of the world of the forms, also serves his theory of the soul. Perfect forms, such as equality, are knowable a priori; we have no need for experience to tell us whether two lines are equal length. We must, therefore, know these things through recollection of these perfect forms. Therefore, the soul must have pre-existed the body to know these facts a priori.
Plato’s argument from opposites was based on his idea that everything in the observable world has an opposite effect. As Plato writes in his work Phaedo; "If something smaller comes to be it will come from something larger before, which became smaller". In other words everything we can know has an opposite; asleep and awake; hot and cold. Similarly they are reversible, just as one goes from a state of sleep to a state of being awake, one can do the opposite. Plato argued that if this were the case, then the same should apply to life and death. Just as one can go from life to death, one must be able to go from death to life; and if this statement is correct, then the soul must survive this transition and as a consequence possess immortality and separation from the body. He believed that animation and life was integral to the very notion of the soul, just like heat is a part of fire; thus it cannot be destroyed and is eternal. “What is it that, when present in a body, makes it living? — A soul.” (Socrates Phaedrus).
A separate argument from his theory of opposites was that of a similar theory of the forms and their opposites. He stated that no entity can consist of contradictory forms, and thus one form must necessarily exist and the other not in any particular entity. The number five cannot possess both the form of even and odd; by adding or subtracting one, the form of odd is displaced by even. Plato wrote: "so fire as the cold approaches, will either go away or be destroyed; it will never venture to admit coldness and remain what it was, fire and cold". The soul must share in the form of life, for we know that those living have a soul. Therefore, it cannot contain the form of death also, for this would be in direct conflict of life. The soul must ontologically necessarily exist, and must therefore be immortal.
In book four, Plato introduces the idea of a tripartite soul based on the idea of singular opposites. As aforementioned, Plato argued that no single entity can have conflicting and opposite states assigned to a single part of it. To desire and to be averse are two conflicting and opposite states; yet it is evident that these two states exist with the human pysche. Socrates used the example of wanting to drink, but choosing not to drink and being averse to it on some calculated and reasoned decision. He concluded that the soul must have two parts; reason and desire. The human soul however also has the characteristic of spiritedness or emotion, and he believed this also to be an integral part of the soul. Plato describes reason as being, by its very nature, attached to knowledge and wisdom, yet also concerned with bodily needs through the souls appetites. Socrates said that spirit was concerned with honour, esteem and the concern of others; and when its desires are not fulfilled it portrays emotion such as anger or indignation. In a corrupt soul, the spirit itself is corrupted and turns against reason; for normally spirit would said to be allied with reason and its function to resolve disputes between reason and desires. Desires on the other hand tend to be concerned with simple and immediate objects which it deems will bring pleasure, such as food, material objects and sex. Desire is, however, able to practise self-discipline as a virtue. Plato utilises an analogy of a chariot, whereby the charioteer represents reason; the good, strong and noble horse symbolises spirit, and the dark, corruptible horse is desire. When the chariot is properly controlled by reason, it stays aloft and may delve into the world of the forms to gain wisdom and knowledge; however if the horses are not controlled then it will plummet to earth and will be kept there in material form until the desires are again controlled. Plato stated that the souls which experienced most knowledge are incarnated as philosophers. Through control and practical application of reason, Plato believed in dependent reincarnation. The soul of a philosopher would escape the continuous state of birth and death and rebirth and would return to the world of the forms; however he was unclear whether that soul could once again plummet to earth and be trapped in a mortal body.
For the soul to enter the world of the forms, it must be a simple entity that is flawless and perfect; which Plato argues for in Phaedo. He argues that the soul in itself is inherently perfect and simple and is affiliated with form like quality. Yet this appears to contradict his theory of a complex and tripartite soul. As a consequence to this criticism, Plato put forward the idea of the soul becoming complex when trapped in a material body; but when free exhibiting perfection.
Contemporary analysis of Plato’s views on the soul produces many criticisms; there is a clear chronological confusion as his work progresses; with the soul starting as an unintelligible and non-tangible item, yet progressing to where the soul becomes a complex tripartite entity that is trapped in the material body, yet still longing to enter the world of the forms. Plato demonstrates a contradictory and muddled thought process that attempts to find resolutions for flaws in his thinking. The idea of an imperfect entity entering the perfect realm of the forms is one such logical fallacy in his argument; and he does this by seeking to find reason and justification for his conclusion, rather than seeking a conclusion based on all of his own logic.
However it is important to take note of the fact that Plato was living in a time when thoughts on life after death were undeveloped, and his scientific understanding would have been wholly different to that which we now possess. Similarly all philosophers, scientists and thinker’s thoughts change, adapt and progress throughout their lives, and Plato was evidently not intentionally contradicting himself, but merely correcting previous ideas and creating new stances that he had not yet seen. We see too with Aristotle's apparent clarity of thought on the soul that his theories alter over time. What Aristotle begins with as the premise of a monist theory, of the soul giving function to the body much like cutting to knife, develops over time to distinguish between the intelligent soul and the material body. Perhaps the main area in which it is possible to criticise Plato’s views on the soul is that it relies on the workability of the world of the forms and the idea of a life after death.
If Plato’s theory of the forms were unchallenged and universally accepted then perhaps his theories on the soul would hold far more credibility; however he argues on the grounds of speculation rather than evidence that is empirically verifiable. I believe it is this which makes Plato’s theory on the soul easy to criticise; that in our contemporary and scientific world, it is his theory’s lack of empirically verifiable evidence that lends itself to criticism.