Is the tripartite soul of the Republic an advance over the immortal soul of the Phaedo?
They are certainly two different descriptions of the soul. But it would be difficult to characterize the tripartite Republican soul as an “advance” over the immortal soul of the Phaedo in the sense that it is a “better” understanding of the soul. The two dialogues contain different descriptions of the soul because they are addressed at different issues. There is no particular inconsistency between the two, and certainly no sense in which the Republican soul could be classed as an “advance” in the sense of “better”.
In the Phaedo, one of Plato’s purposes is to “prove” that the soul is immortal. He presents five (approximately, depending on how one divides them up) arguments for the immortality of the soul. One of these arguments likens the soul to a Form because they share so many properties distinct from particulars. In this reasoning, Plato claims (as a flat, unsubstantiated assertion — or premise) that the Forms are uniform, independent, constant, invariable, invisible, immortal, uncreated, and indivisible. Particulars, by comparison, are variable, dependent on the Forms, inconstant, visible, created, and dissoluble. He then proceeds to describe the body as variable (changing from day to day depending on conditions), inconstant (it dies), visible (obviously), created (at birth), and dissoluble (decays to dust when dead) while the soul is (as a matter of common belief, rather than a matter of empirical observation) uniform, independent, constant, invariable, and invisible. Obviously then, he continues, the soul is not a particular but is more like a Form. He then concludes that the soul must actually be a Form and therefore, like other Forms, must have the additional properties of being immortal, uncreated, and indivisible. In elaborating on this theme, Plato explains that the soul is in origin simple and purely rational (like all Forms), and takes on complexity and conflict only as it assumes a body (the way that particulars are merely imperfect reflections of the pure Form they participate in).
In the Republic, on the other hand, Plato’s purpose is to define “justice”. As part of the lengthy exploration of what justice is, he describes the soul as tripartite. In the Republic he says —
“Let’s make an image of the soul . . . model the form of a many-headed monster, having a ring of heads of all manner of beasts, tame and wild, which he is able to generate and change at will . . . now make a second form as of a lion, and a third of a man, making the the first the largest, and the third the smallest . . . now join them, and let the three grow into one . . . next fashion the outside of them into a single image . . . so that he who is not able to look within, and sees only the outer shape, may believe the whole to be a single human being.” Plato, Republic:IX (588c-e)
In the Republic, therefore, Plato has described the soul as having three parts — a “rational” part that gives us wisdom, a “spirited” part that gives us courage, and an “appetitive” part that gives us temperance. Justice, he maintains, is a general virtue that arises when each and every part of the soul performs its proper function within the whole. The notion of justice determines the rightness of human characters and behaviours. Justice is the Form of a good character and a good life — the ideal perfect of which all particulars are imperfect reflections or copies.
In the earlier Phaedo, Plato describes the soul as indivisible because indivisibility is a necessary consequence of his argument that the soul is a Form and therefore immortal. In the later Republic, Plato describes the soul as having three parts, because having three integrated aspects is a necessary consequence of his effort to understand and define “justice”. Some commentators have suggested that this difference represents an inconsistency in Plato’s theory of the soul. The essay’s title question implies the respondent should interpret it as a change or evolution in Plato’s thinking about the soul. But it need not be either of these. And in fact the two descriptions are not inconsistent with each other. One cannot divide a triangle into its three sides and still have a triangle. The triangle remains indivisible (as a triangle) even though it has three sides. Likewise the Platonic Republican soul could have three faces or voices while remaining indivisible as a soul. Even if it happens to be tripartite in composition, the soul need not be tripartite in the sense of ‘part’ that implies an ability of its parts to conflict, or an ability to be taken apart.
So if the Republican soul does not necessarily represent a change in how Plato thought about the soul, it need not represent an “advance” over the immortal soul of the Phaedo in the sense of an improvement.
On the other hand, the quality of the reasoning in the two works is quite different. In the Phaedo, Plato reasons that the soul is immortal and indivisible from more fundamental premises. In the Republic, Plato simply takes as given that the soul has three parts in his exploration of justice. From this perspective, one can observe that reasoning in the Phaedo demonstrating that the soul is immortal is very poor, while the simple premise of the Republic has no reasoning that could be faulty. On this rather different basis, one could suggest that the tripartite soul of the Republic is indeed an advance over the immortal soul of the Phaedo
The Phaedo is generally considered significant for the arguments that Plato offers to “prove” that the soul is immortal. However, it is the flawed reasoning of these that make it difficult to know whether Plato actually intends the Phaedo as a serious philosophical work, or as a satirical spoof of the Socratic method. Or possibly a satirical spoof of the dialectic methods of the Sophists. Even granting the unquestioned premise of body-soul duality (natural enough given Plato’s cultural context), and even excusing the completely anti-empirical view of learning adopted by Plato, all of the arguments presented in this dialogue are laughably incomplete, and unacceptable by any standard of logical analysis. Each of the arguments presented very obviously commits the fallacy of assuming the consequent. Considering how tightly reasoned are Plato’s arguments on other topics in other dialogues, it is hard to regard these efforts as serious philosophical reasoning. Especially considering that the Phaedo is usually classified by chronologists as one of the middle or transitional works, and not as one of Plato’s earlier efforts.
In his Argument from Forms, to give just one example, Plato draws upon the presumed resemblance between a Form and the Soul. To do so, of course, he is drawing upon the then culturally extant popular beliefs in the body-soul dichotomy (the independence of the soul from the body), and the beliefs that the soul is perfect (constant and invariable), and immaterial (invisible). He then argues that the soul therefore necessarily must possess the all the other presumed properties of a Form rather than any of the properties of a Particular. He is arguing that because it is popularly accepted that the soul possesses some of the properties he attributes to Forms, it therefore must possess all the other properties (such as immortality) that he attributes to Forms. In the next step, Plato extends this reasoning by slipping quietly from maintaining that a soul exhibits some of the properties of a Form, to claiming the soul is itself a Form. As Aristotle would later point out, this is an invalid move in deductive logic. Plato commits the syllogistic fallacy of the undistributed middle. However, aside from the logical fallacy involved, the entire argument is based on the preconceived notion (based on the then popular cultural milieu) that the soul has certain properties — specifically those properties shared by Forms. And it is based on the fallacious analogical reasoning that if it shares some of those properties, it necessarily must share them all. The reasoning also depends, of course, on the presumption that Forms possess the equivalent kind of existence as it is presumed a soul possesses (“real” rather than a merely conceptual existence, for example). The entire structure of reasoning crumbles to naught if one fails to accept any of Plato’s critical and unchallenged premises — the recollection theory of knowledge; the theory of forms; the properties of forms; and the properties of souls.
So, unless one considers the Phaedo as either a capture of actual Socratic logical error, or a very early Platonic attempt at reasoning (contradicting the chronology of the experts), one has to wonder at the glaringly obvious flaws in the arguments. Perhaps it is not actually intended to be a serious logical effort. Perhaps it is intended as a display of many of the dialectical persuasive tricks of the Sophists, rather than a display of carefully rational reasoning.
Clearly then, when considered as elements of logical reasoning, one would have to conclude that the simple description of the soul as tripartite in the Republic is indeed an advance over the very flawed logic employed to “prove” the soul is immortal in the Phaedo.