Plato in Republic reasoned that if the human soul is a unified entity of some sort, then it would not be possible to account for the phenomenon of incontinence or akrasia. For as a unified entity, the soul would be the source of every desire. So, on pain of self-contradiction, one could not assert that someone wanted and did not want the same thing at the same time. And yet, that is precisely what akrasia seems to be: one desires to do something and simultaneously desires that the first desire not be effective. How is something at once so depressingly commonplace and yet so seemingly bizarre to be explained? By postulating parts or divisions of the soul such that it is true that only one of these parts has the initial desire and another one has the opposing desire. Yet with the postulation of such parts, come a host of problems knotty enough to inspire thousands of pages of analysis by virtually all the major philosophers of antiquity and into the Middle Ages and beyond.
Consider just the major problems. If the soul is divided into parts, whence the unity of the person or subject? If the person is to be identified with one of the parts, then who gets ownership of the rest? If it is identified with none of the parts, in what sense is any desire the desire of the person? Further, if the soul is not a corporeal entity and if “parts” is a term primarily applied to corporeal magnitudes, then are the soul’s parts only metaphorical parts? If so, how does partitioning explain akrasia? If they are supposed to be real parts, sufficient to do their intended work, how can incorporeal entities have them? A triangle has parts, say, its lines and angles, but in no sense are these capable of being opposed to each other, at least not in the relevant sense. Further, if the putative parts are supposed to explain the phenomenon, then at least one of these must be other than the part which reasons to conclusion that the desire is to be resisted. Are we then to say that one of the parts is not rational or even irrational? How does this possibility comport with the claim that rationality is what defines the human soul? Finally, if one or more of the parts is a source of desires that cannot occur without a body, for example, a desire to eat, what then are we to make of the possibility of the immortality of the soul? Are the body-implicating parts capable of existing apart from the body? If so, how? If not, how is that which is immortal supposed to be related to the embodied desiring person or self?
In the face of such problems, it is hardly surprising that some philosophers would insist on repudiating their source, namely, the claim that the phenomenon of akrasia is real. No incontinence, no need to concoct strange theories about personhood or selfhood to account for it. This was, of course, the strategy of the Old Stoa, independently motivated by a principled materialism that refused to entertain the possibility of “parts” of a non-existent incorporeal entity. It is not that the Stoics needed to deny the partitioning of the soul any more than they needed to deny the partitioning of the hand into fingers. It is just that they refused to condone opposing parts, insisting rather on a unified material subject. Thus, the philosophical history of the partitioning of the soul in antiquity and beyond is comprised of one thread identified with the responses to the Platonic problematic and another with responses to the Stoic materialist challenge.
The collection of papers, edited by Klaus Corcilius and Dominik Perler, contains eleven papers, six on ancient philosophers (Plato, Aristotle, Stoicism, Galen, Plotinus, and the post-Plotinian Neo-Platonists), two on medieval scholastics (Ockham and Suarez), and three on early modern philosophers (Descartes, Spinoza, and Leibniz). The papers are uniformly rich in content and subtle in argument. It is impossible here discuss the arguments in any detail. The first six papers have a unity provided by the two poles of Platonism and Stoic materialism. The last five add an additional layer of complexity owing to the introduction of Christian doctrine on immortality and resurrection, and in the case of the last three, yet further complexities owing to the interaction of philosophy and the new physics of the 17th century. All together, the book could be the basis of an exciting graduate or upper-level undergraduate course, though I imagine it would be one that required the expertise of more than one instructor! Here is only the briefest summary of the contents of each of these papers.
The paper by Christopher Shields, “Plato’s Divided Soul,” obviously has a critical role in articulating the terrain over which the subjects of the rest of the papers are going to do battle. Shields claims that the sense in which Plato argues for the partitioning of the soul is not a sense according to which the soul has compositional parts that threaten to become homunculi; rather, it has aspectual parts, meaning that its phenomenologically diverse or even opposing desires are in fact “aspects” or features or properties of the one, unified agent or soul. Thus, the puzzling conflicts are within the agent, not among agents. Although one might well wonder whether this interpretation accounts for the synchronous psychological conflict that Plato describes in Republic, the paper nicely reveals the challenges faced by later thinkers who are resolved to acknowledge a stronger sense of psychical “compositionality.”
Thomas Johansen’s “Parts in Aristotle’s Definition of the Soul: De Anima Books 1 and II” focuses on Aristotle’s faculty psychology to argue that for him parts of the soul are to be understood as an integrated hierarchy of functions, different according to different species of animals. The unity of these parts is accounted for by the dominant role of the defining psychical function. Thus, for human beings, all of our psychical functions are unified by our rational faculty. As the Stoics grasped, this is a powerful approach to agential unity. Accordingly, when in Nicomachean Ethics the phenomenon of incontinence is addressed, one can see Aristotle tending towards a view made explicit by the Stoics, namely, that what appears to be oppositional conflict within the soul is really an indication of its malfunctioning.
Brad Inwood in “Walking and Talking: Reflections on the Divisions of the Soul in Stoicism” explains that the position of the Old Stoa (and to a certain extent that of the so-called Middle Stoa of Panaetius and Posidonius) is in fact a fusion of a faculty psychology (whether Aristotelian or not) where an integrated psychical hierarchy is dominated by rational functionality and a commitment to a sophisticated materialism. The parts of the Stoic soul really are material parts, in opposition to the Platonic and Aristotelian position that the immaterial soul parts or functions operate in or are manifested in different parts of the body. Hence, incontinence is in principle impossible. The “leading part of the soul” or hēgēmonikon is the unique agent. And psychical conflict, since it is the malfunctioning of the rational faculty, is actually a kind of irrationality.
In “Partitioning the Soul: Galen on the Anatomy of the Psychic Functions and Mental Illness,” James Hankinson examines Galen’s rather eccentric Platonism in the context of his revolutionary medical scientific work. As an anatomist, Galen was more concerned to locate precisely the organs of psychical functionality than to theorize about the substantial nature of the unitary soul thus revealed. Hence, his agnosticism about the immortality of the soul. On the other hand, against the Stoics, Galen argued that there were indeed appetitive and spirited parts of the soul neither reducible to the rational part nor subordinated to it. And yet the treatment of malfunctioning in these parts is medical treatment of bodily parts. Hence, it turns out that incontinence is a form of mental illness. This last point is broached by Plato himself in Timaeus, and its development reaches into contemporary discussions of the intersection of psychology and ethics.
Plotinus is almost the polar opposite of Galen in his reflections on Plato’s partitioning of the soul. For, as Filip Karfik shows in his paper “Parts of the Soul in Plotinus,” these reflections are firmly situated in a large and complex metaphysical framework. Thus, the parts of the embodied soul can only be understood as images and, hence, defective versions of the fundamental hypostases of Intellect and Soul. Plotinus’ distinctive contribution to the resolution of the Platonic problematic is to argue that the unifying factor for the embodied tripartite soul is the undescended intellect of each individual disassociation from which is the source of incontinence and vice. What turns up as psychical weakness and disarray is owing to the adventitious or ephemeral nature of embodied subjectivity.
The paper by Christoph Helmig, “Iamblichus, Proclus and Philoponus on Parts, Capacities and Ousiai of the Soul and the Notion of Life” is a fine complement to the paper by Karfik, showing how later Platonists followed Plotinus in situating psychology within a distinctively Platonic metaphysics. But unlike Plotinus, these philosophers eschewed the Plotinian solution to the problem of unity by positing undescended intellects. Evidently, the immortality of the soul is sufficient to guarantee its unity, this despite embodiment being an alienating condition. I found intriguing Helmig’s suggestion that, counter to the common scholarly view, the late Platonic metaphysical account of embodied psychology does not, or at least was not thought by these Platonists, to constitute a repudiation of Aristotle.
The two papers by Dominik Perler, “Ockham on Emotions in the Divided Soul” and by Christopher Shields, “Virtual Presence: Psychic Mereology in Francisco Suárez” provide a nice contrast in the late Scholastic debate regarding embodied human psychology. Whereas Ockham took the well-established faculty psychology to imply a plurality of souls. In particular, he distinguished between “sensory emotions” and “volitional emotions.” Only the latter are under the control of the rational soul and as a result, the former belong to an additional soul. This position strongly reflects the Platonic argument for partitioning of the soul. The plurality of souls are really a plurality of subjects. Suárez hit upon an idea that is already present in late Platonic thinking, namely, the idea of “virtuality” that is, the presence of lower faculties in the higher rational faculty in the sense that its various powers can be manifested in different circumstances without thereby compromising the unity of the soul. That is, the higher contains the lower in the sense in which a cause contains its effects. The “top-down” metaphysics of Platonism long before Suárez deployed this concept in multifarious ways.
The three papers on early modern philosophers present a variety of new arguments inspired, I think, by the new physics of the 17th century. Marleen Rozemond’s “The Face of Simplicity in Descartes’s Soul” provides a nice contrast to the papers on Plato and Plotinus in that it clearly shows that the so-called Cartesian dualism is not the dualism of ancient philosophy. For Descartes, psychical conflict is really a conflict between body and soul, not among putative parts of the soul itself. Thus, Descartes ignores the complex argument of Plato’s Republic to return to what appears to be the relatively crude body/soul dualism of Phaedo. Stephen Schmid’s “Spinoza on the Unity of Will and Intellect” provides an analysis of Spinoza’s radical claim that, not only does the soul not have faculties or powers, but there is in it no distinction between intellect and will. Schmid sees Spinoza’s monism as a radicalization of Descartes, but it seems to me to be a radicalization of Stoic naturalism as well. Christian Barth, in his “The Great Chain of Souls: Leibniz on Soul Unitarianism and Soul Kinds,” takes Leibniz’s account of the soul as a sort of reformed Thomism, according to which the faculties of souls, which for Thomas are rooted in his Aristotelian hylomorphism, are effaced in favor of “inner activities” of immaterial souls, correlated with but not causing or being caused by their bodies. In particular, these psychical activities are all representations of bodily activities. This includes all non-rational activities. Barth helps us see in Leibniz the distinctively modern representationalist epistemology as central to accounts of the soul.
Altogether, a challenging and very worthwhile collection of articles.