Plato's Argument For The Existence Of Forms

The passage from 72e to 77a in Plato’s Phaedo contains Plato’s argument for the idea that the soul exists before birth. This argument relies heavily on Plato’s Theory of Forms. For Plato, the sensory, material world is full of impermanence, instability, contradiction, and illusion. Therefore, Plato says, for knowledge to be possible, there must be a realm of objects, namely “Forms”, which exist outside of the spatiotemporal realm, and which mediate our knowledge of the sensory world. These Forms are more real than objects in the sensory realm, and they are permanent, stable, unchanging. To argue for the existence of Forms, Plato gives an example of a piece of wood A, which is equal to another piece of wood, B, and which we understand as an instance of equality. However, he points out a third piece of wood, C, which A is unequal to. Therefore, even though A and B give us the idea of Equality, neither of them can
actually be Equality, since that would mean that Equality was unequal. But if neither A nor B are Equality, but each brings Equality to mind, there must be some further object, absolute Equality, by which A and B make Equality come to mind. However, this Equality cannot be any sensory instance of equality, because every such instance would succumb to the same problem we encountered with the pieces of wood. It must instead by a Form, which is permanent, stable, eternal, etc (74a -74c). However, we possess knowledge of such Forms, we must ask ourselves where this knowledge came from.
Since this knowledge cannot come from the senses (since no sensory objects are the Equal), it must come to us through some other avenue. Since we have always known of Equality, but we could never have learned it from some sensory experience, we must have been born with this knowledge, which implies that we knew of Equality, and the other forms, before we were born. This means that during our life, when we seem to be learning about the Forms, we are not actually acquiring this knowledge for the first time (since, as was shown, knowledge of Forms is not acquired through the senses); instead, what appears to be learning is a recollection of what we knew before our birth (75a-75c). All knowledge is present within oneself, and one can be guided towards the answer or a solution, but to truly learn something one needs to fully be able to understand the concept and relate it to previous knowledge or experience, and make that knowledge truly yours by grasping
it. One of the most problematic aspects of this passage is that it is difficult to make sense of Plato’s notion of Forms in a coherent way, which can be shown through his treatment of Equality. Ordinarily our understanding of equality is such that an object does not possess equality inherently, but only in relation to some other thing. If this is true, then the Form of Equality can likewise only be understood in its relation to other things. This is because if the Form of Equality were only understood as an inherent quality of Equality, it would be so different from ordinary uses of the concept of equality that it would be difficult to account for why the Form of Equality mediates our understanding of ordinary equality. But if this is true, then the Form of Equality cannot have the properties that Plato attributes to it, namely the quality of always being equal and never unequal. This is because the Form of Equality differs from other forms, such as the Form of Saltiness, which would thereby make it unequal. But the idea that the Form of Equality is always equal and never unequal is the reason why the idea of Forms was invoked in the first place. Therefore, the theory of Forms is in trouble, and Plato can no longer use it to argue for the pre-existence of the soul, hence making it an invalid argument since not all the premises turn to be true, thus the conclusion is not true also. Since the argument is invalid, it is also unsound, as the argument is only sound if it is valid and all premises are true.