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The Soul as an Idea in Ancient Greece 101: Aristotle’s Psychology


The concept of the soul has long fascinated humanity, occupying a central place in the collective consciousness. In the framework of ancient Greek history of thought, the notions of it formed a vibrant and evolving tapestry. The ideas surrounding the soul that emerged from ancient Greek thought exerted a profound influence on subsequent intellectual developments, particularly within the realm of Christianity and Western European philosophy. From the Scholastic thinkers of the Middle Ages to the Renaissance humanists and the Enlightenment philosophers, the soul remained a focal point of inquiry and speculation. Even in modern times, the legacy of the Greek understanding of the soul persists, shaping the contemporary conceptions and debates. The exploration of consciousness, the mind-body problem, and ethical considerations all bear traces of the enduring influence of Greek philosophy on the existent beliefs on the matter.

This series of articles seeks to explore the multifaceted concept of the soul in ancient Greek literary, ritual, and philosophical traditions. Beginning with foundational literary works such as those of Homer and Hesiod and progressing through the profound theories put forth by philosophers like Plato, Aristotle, and others, it aims to unravel the diverse and evolving understanding of the soul in ancient Greece.

The series is divided into the following chapters:

5. The Soul as an Idea in Ancient Greece 101: Aristotle’s Psychology

6. The Soul as an Idea in Ancient Greece 101: Epicurus’ Soul Atoms

7. The Soul as an Idea in Ancient Greece 101: The Air and Fire of Pneuma

8. The Soul as an Idea in Ancient Greece 101: Plotinus and Neoplatonism

The Soul as an Idea in Ancient Greece 101: Aristotle’s Psychology

Navigating through the landscape of ancient philosophical thought, attention turns inevitably to Aristotle (384–322 BCE), a seminal figure originating from Macedon but based in Athens for most of his adult life. Aristotle uniquely integrated the realms of philosophy and science, venturing far beyond mere theoretical discourse to include rigorous empirical investigation. Aristotle's contributions to the field of psychology are encapsulated primarily in two major works: De Anima (On the Soul) and the collective treatises known as Parva Naturalia (Short Treatises on Nature), which also encompass other noteworthy contributions like De Sensu (On Sense) and De Memoria (On Memory). The central thesis of this chapter posits that Aristotle's approach to psychology established a distinctive conceptual foundation for the understanding of the soul, thereby diverging markedly from the views of his predecessors. Of particular significance is De Anima, a work that grapples with fundamental questions related to the material basis of psychological states. In the work, Aristotle raises a pivotal inquiry: Are all psychological states essentially material conditions of the body? This question aligns closely with broader metaphysical concerns and bears directly upon his scientific interests in biological classification (Shields, 2020).

A crucial aspect of Aristotle’s psychological framework is its broad range. Aristotle defines psychology as the branch of science responsible for investigating the soul as the general principle of life. Thus, the scope of his inquiry is not confined to human beings but extends to all living organisms, including plants and animals. This breadth of focus is indicative of his biological proclivities and offers further testimony to his comprehensive metaphysical examination. Furthermore, the methodology employed in Aristotle's psychological works incites considerable academic debate. While Aristotle categorises the study of psychological states like anger or joy under natural science, owing to their evident corporeal connections, he simultaneously casts doubt upon whether the intellect (or intelligence)—noûs—can be so easily classified. Given this multi-layered complexity and comprehensive scope, Aristotle’s work serves as both a culmination of previous philosophical contributions and a foundational basis for future investigations into the concept of the soul. Through an empirical yet philosophically enriched approach, his works offer an understanding that transcends disciplinary boundaries, contributing significantly to the scholarly discourse on this elusive yet fundamental entity—the soul (Shields, 2020).

Figure 1: Relief of Aristotle and Plato (della Robbia, 1437–39).

In crafting his philosophy of the soul, Aristotle delves into the concept of what constitutes a "natural body," a notion that sometimes stands in contrast to the ideas presented by his philosophical predecessors, including Plato. In Aristotle's view, natural bodies are distinct from artificial ones due to their intrinsic principle of motion and rest, meaning they contain within themselves the reasons for their changes or states of stability. Thus, there is a definitional linkage between the body and its inner cause of changes, which Aristotle identifies as the soul. This understanding sharply contrasts with Plato's perspective. Plato, in Aristotle’s interpretation, seems to attach the soul to any given body somewhat arbitrarily. This makes Plato's concept of the soul-body relationship appear disconnected and perhaps implies that, in Plato's framework, the bodies of living beings might not fully qualify as "natural" in the way Aristotle understands the term. For Aristotle, the soul is not just an internal inhabitant of the body; it is deeply integrated with the body, defining its very nature and potentialities (Johansen, 2016).

The Concept of Hylomorphism

The interpretation of Aristotle's concept of the soul is laden with complexities, partly due to the philosophical context in which he lived and worked. Aristotle's era, the 4th century BCE, was a vibrant period in ancient Greece, marked by groundbreaking advances in various fields including philosophy, science, and politics. Athens was a hub of intellectual and cultural activity, and philosophers who preceded Aristotle had already paved the way with their discussions on the nature of knowledge, existence, and the human soul. Building on this legacy, Aristotle developed a unique understanding of the soul, or psūkhḗ, which encompassed not just humans but all living beings. This diverges from modern perspectives, for instance, which might entertain the notion of artificial intelligence having consciousness but find the idea of plants possessing mental life far-fetched. In De Anima Aristotle aims to identify both the nature of the soul and a comprehensive description that applies to all kinds of souls. Although Aristotle's discourse can appear abstract, it sets forth a framework for a credible interpretation. He introduces a two-tiered approach to understanding the soul: initially as an actualisation, and subsequently as an essence (Miller, 1999).

Figure 2: Bust of Aristotle (After Lysippos, after 330 BCE).

The term actualisation can be contextualised by looking at Aristotle’s hylomorphic theory, which considers all beings as composites of form (morphḗ) and matter (hū́lē). Within this schema, actualisation should not be viewed in isolation but in relation to potentiality. Matter is seen as the seat of potentiality, a kind of dormant or latent capacity. On the other hand, form serves as the actualising principle that transforms this latent capacity into a concrete, identifiable reality. Thus, when Aristotle describes the soul as an "actualisation," he implies that the soul serves as the form that brings the body's potentialities to life. It is the principle that activates the intrinsic capacities of an organic, natural body, thereby making it "alive." This marks the first stage in Aristotle's understanding of the soul (Miller, 1999).

The second stage of Aristotle's account stresses the soul as the "essence" of a natural body. Here, Aristotle employs analogies to expound his point. He suggests that if an axe were a natural body, its soul would be what makes it an axe in essence; it is the "axeness" so to speak. Separated from this essence, it would not genuinely be an axe anymore, but merely resemble one. An axe, however, is not a natural body, so it does not have a soul, but the example emphasises the necessity of the soul’s function in identifying the "being" of a particular natural body. Another analogy involves the eye. If the eye were an animal, its sight would be its soul. This is because sight represents the essence of the eye, defining its function and nature. Remove sight, and the eye is no longer genuinely an eye, much like the axe losing its ability to cut. To extend this to the broader picture, Aristotle posits that the soul is to the body what sight is to the eye—an intrinsic essence without which the body loses its "bodyness." Thus, according to Aristotle, the soul is not just a separate entity inhabiting the body, but rather the essence that defines what it means for that body to be alive (Miller, 1999).

Figure 3: Aristotle (de Ribera, 1637).

In Aristotle's exploration of the soul-body relationship, he employs the metaphor of the soul being to the body as the shape of Hermes is to bronze. Here, the reference to Hermes, the Greek messenger god, serves as an illustrative analogy rather than a theological statement. The shape that a statue of Hermes takes is contingent upon the bronze that serves as its material basis. In much the same way, Aristotle believes that the soul acts as the defining "shape" or "form" that gives the body its particular identity and function. This analogy is crucial in understanding Aristotle's position, which challenges the existing philosophical dichotomies between materialists, who hold that mental states are merely physical states, and substance dualists, who believe that the soul can exist separately from the body. Aristotle steers the discussion away from these binary oppositions by suggesting that the wrong questions are being asked. Instead of fretting over whether the soul and body are one, one should look at it as they look at other composites, like a house made of bricks and mortar. Each part is essential for the structure to be what it is, yet they are not identical. This approach also has implications for the concept of the soul's separability from the body. Yet, Aristotle leaves room for exceptions, noting that some parts of the soul might not be as closely tied to the body. By doing so, Aristotle does not just settle the debate between materialism and dualism but adds another layer of complexity, suggesting that these are not the only options available when contemplating the enigma of the soul-body relationship (Shields, 2020).

Furthermore, attention should be drawn to the fact that Aristotle presents the intricate concept regarding the soul's unity with the body, which is not just a superficial connection with the visibly organic form. Instead, he emphasises the soul's profound bond with what he terms the instrumental body. This instrumental body serves a dual purpose: it is an extension of the soul for perceiving the world around it and also its means for movement. This idea challenges simpler interpretations of the soul-body relationship, suggesting a layered, symbiotic association where the soul actively uses the body as a tool for both perception and motion (Bos, 2012).

Figure 4: Double-sided herm of Aristotle (Anonymous, ca. 325-300 BCE).

The Functions and the Faculties of the Soul

In De Anima, Aristotle embarks on a comprehensive study of the soul’s various capacities or faculties. At the core of his exploration are three principal faculties: nutrition, perception, and intellect, with the later introduction of the faculty of desire. These capacities serve as the building blocks in his hierarchical model of living beings. All living entities possess the faculty of nutrition, which is the broadest of all. Animals, in addition to nutrition, have the gift of perception, while humans are endowed with all three––nutrition, perception, and mind.

Nutrition, as Aristotle outlines, is the most fundamental of these faculties. Every living entity grows, matures, and eventually declines, a process impossible without the nutritive capacity. He provides a detailed analysis of this faculty, starting from its very basics:

The nutritive soul belongs to other living things as well as man, being the first and most widely distributed faculty, in virtue of which all things possess life. Its functions are reproduction and assimilation of nutriment. For it is the most natural function in all living things, if perfect and not defective or spontaneously generated, to reproduce their species; animal producing animal and plant plant, in order that they may, so far as they can, share in the eternal and the divine. (Aristotle, De Anima ii 4, 415a23-b1)

This deep dive into the concept of nutrition leads Aristotle to challenge reductive interpretations of life. For Aristotle, life isn't merely a mechanical process that can be explained by the tendencies of material elements. Instead, he argues that growth in organisms follows a specific pattern, a direction stemming from the soul, which cannot be purely explained in materialistic terms. This discussion on nutrition sets the tone for Aristotle's approach to the other faculties of the soul. He consistently seeks to elucidate the nature of each faculty while questioning the feasibility of reductive explanations (Shields, 2020).

Figure 5: Aristotle with a Bust of Homer (Rembrandt, 1653).

In Aristotle's philosophical examinations, his hylomorphic conceptualisation of perception stands as a pivotal exploration, distinguishing animals from other life forms. Predicated on the marriage of matter and form, Aristotle argues that the ability to perceive is a defining feature of animals. Every animate being, in his view, inherently possesses the capability of perception; with touch as the fundamental sensory modality, supplemented by other senses in most species. Such a faculty, Aristotle argues, is not a mere incidental trait but rather serves profound teleological (directed towards an ultimate aim) purposes. For animals, perception becomes an indispensable tool, facilitating crucial life functions such as navigation, sustenance, and reproduction. Aristotle theorises that perception transpires when an organ undergoes alteration due to its interaction with an external object. This interaction is not arbitrary. It necessitates a correspondence between the affecting object (agent) and the perceptive capacity or organ (patient). In the act of perception, the perceiver is not merely affected but receives the "form" of the perceived, echoing a kind of form-matter duality. Yet, this reception is contingent on the suitability of the recipient; specific changes necessitate specific capacities. A profound contention in Aristotle's discourse is the principle of isomorphism in perception, suggesting a reflection or representation between the perceiver and the perceived. The extent of this reflection has been debated by scholars, ranging from a direct mirror-like representation to more symbolic interpretations (Shields, 2020).

Aristotle portrays the intellect as the segment of the soul responsible for knowledge and understanding. For him, it is innate to humans to crave knowledge, making the presence of an intellect pivotal to being human: "All men naturally desire knowledge" (Aristotle, Metaphysics, 1.980a).

Human intellect is also instrumental in planning, deliberating, and conceptualising strategies. Hence, Aristotle differentiates between the "practical intellect", which concerns action, and the "theoretical intellect" focused on contemplation and understanding. Aristotle likens thinking to the process of perception: just as one’s senses receive a specific form from the external world, the intellect receives an intelligible form from the object of thought. So, when one thinks, their intellect becomes "shaped" or "informed" by what they are contemplating. However, while the intellect perceives forms, it doesn't become those forms. For instance, when we think of a stone, our intellect doesn't turn into a stone; it grasps the essence or form of the stone. Aristotle suggests that the intellect generally perceives universals (like the concept of a stone) rather than particulars (a specific stone). An important aspect of Aristotle's idea is that the act of thinking aligns the structure of the intellect with the structural features of the object of thought (Shields, 2020).

Figure 6: Aristoteles (van Gent, circa 1476).

The distinction between perception and intellect crucially lies in their objects: perception grapples with the tangible material, while intellect interacts with the intangible universal. This dichotomy raises a conundrum when considering entities that are material yet are not solely defined by their material nature, like a person. Analysing Aristotle’s work Eve Rabinoff (2015), an expert in ancient philosophy, presents an insightful argument against the stance which suggests that one perceives certain configurations (like colours and shapes) and then interprets these perceptions to understand concrete entities. Contrary to this, Rabinoff posits that humans do not merely interpret what they grasp with their senses but truly understand it. The human perception, therefore, is intelligible on its own without the need for a separate act of interpretation. This signifies that while animals may comprehend things as they physically appear, humans have a heightened perception, imbued with understanding, allowing us to perceive entities for what they inherently are. Rabinoff further elaborates that intellect shapes human senses, not in an interpretative manner, but in a way that aids understanding. This distinction underlines a significant difference between human and nonrational animal perception.

Furthermore, Aristotle makes a provocative shift in De Anima iii 5 regarding the active intellect, a striking feature of which is its purported separability and immortality—traits that seem to be in stark contrast with his earlier treatment of the mind as one of the faculties of the soul, which he considered inseparable from the body. A possible avenue for reconciling these seemingly disparate accounts lies in the multi-faceted nature of intellect (or mind) that Aristotle seems to imply. If it has an aspect that is inherently divine and separable—able to maintain its activity apart from bodily conditions—this could resolve the seeming contradiction. Here, the concept of "separability in being," rather than "separability in account," is instrumental. The former suggests a fundamental autonomy, implying that intellect, as a unique power of the soul, has the potential for a form of existence independent of the body (Cohoe, 2022).

Figure 7: Aristoteles (After Lysippos, 1st or 2nd century CE).

Aristotle's conceptualisation of the soul in the De Anima offers a detailed framework that aligns the soul with the system of active abilities inherent in animate organisms. His theory traverses the complexities of soul-body dynamics, laying emphasis on the soul as neither a corporeal entity nor an abstract form isolated from bodily functions. Rather, it serves as a principle that accounts for the rest and change in living bodies, acting as an integrative force that connects diverse vital functions ranging from metabolism to cognition. Aristotle diverges from Platonic ideas by contending that even human souls cannot exist or operate independently of the body. He counters the need for a special metaphysical treatment for mental functions by considering them in the same vein as other vital functions. This inclusivity does not diminish the distinctiveness of mental activities but rather reinforces the idea that they, too, can be comprehended through natural principles that explain all phenomena. Importantly, Aristotle's ideas leave room for isolating mental functions for special inquiry if required, without violating the conceptual integrity of his overall theory.

A remarkable aspect of Aristotle's theory is its ability to situate mental and physical functions within the same explanatory system without conflating them. It harmonises the dualism between form and matter, suggesting that an ensouled body is essentially in-formed matter. The soul becomes the nexus through which different facets of living experience are unified, functioning as a set of abilities tailored to the structure and complexity of the organism in question. In essence, Aristotle's theory acts as a means of balancing the corporeal and incorporeal aspects of existence. By attributing the soul's diverse roles to its active abilities, his theory resists dividing vital functions into "higher" and "lower" categories but instead envisages a cohesive, unified system. Thus, the Aristotelian framework not only addresses the multi-dimensional aspects of the soul but also provides a model for understanding life processes as interrelated manifestations of the soul's governing principles. This integrated approach stands as a testament to the comprehensive depth and flexibility of Aristotle's thinking, offering a rich tapestry for analysing the relationships between the soul, body, and the natural world.

Bibliographical References

Aristotle. (1933, 1989). Aristotle in 23 Volumes, Vols. 17, 18 (H. Tredennick, Trans.). Harvard University Press; William Heinemann Ltd.

Bolton, R. (1978). Aristotle's definitions of the soul: "De Anima" ii, 1-3. Phronesis, 23(3), 258-278. Brill.

Bos, A. P. (2012). Aristotle's definition of the soul: Why was it misunderstood for centuries? The dubious lines Anim. II 1, 412b1–4. Museum Helveticum, 69(2), 140-155. Schwabe Verlagsgruppe AG.

Cohoe, C. (2022). The Separability of Nous. In C. Cohoe (Ed.), Aristotle's On the Soul: A Critical Guide (Cambridge Critical Guides, pp. 229-246). Cambridge University Press.

Hicks, R. D., & Aristotle (1907). Aristotle: De Anima. Cambridge University.

Johansen, T. K. (2016). Natural bodies in Plato and Aristotle. In T. Buchheim, D. Meißner, & N. Wachsmann (Eds.), Archiv für Begriffsgeschichte, Sonderheft 13 (pp. 455-470). De Gruyter.

Miller, F. D. (1999). Aristotle's philosophy of soul. The Review of Metaphysics, 53(2), 309-337. Philosophy Education Society Inc.

Rabinoff, E. (2015). Aristotle on the intelligibility of perception. The Review of Metaphysics, 68(4), 719-740. Philosophy Education Society Inc.

Shields, C. (2020). Aristotle’s psychology. In E. N. Zalta (Ed.), The Stanford Encyclopedia of Philosophy (Winter 2020 ed.).

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