Plato and Aristotle on Knowledge, Reality, and Metaphysics

Introduction: Two Pillars of Western Philosophy

Plato and Aristotle are arguably the two most important philosophers in Western history. Although they were not necessarily the earliest thinkers to consider questions of epistemology and ontology, they were arguably the first to attempt to order their considerations of these questions into quasi-scientific systems. Although subsequent scientific research has rendered many of their more self-assured pronouncements obsolete or even laughably incorrect, their work remains essential for understanding the development of Western thought. By examining some of their most notable theories and discussions, and by comparing and contrasting their work, one can see how contemporary concepts of knowledge, being, individuality, and reality ultimately stem from the contributions of these two thinkers.

Both Plato and Aristotle concern themselves with the realm of metaphysics, which automatically makes discussing their ideas somewhat problematic, because by definition there is no empirical evidence for anything metaphysical. The only evidence available to humans is physical, since even logical deductions and inferences first depend on observations of physical phenomena. Thus, in a sense there is no such thing as metaphysics — yet this has not stopped philosophers, theologians, and others from constructing elaborate systems of meaning intended to either demonstrate or justify belief in the metaphysical. In the case of both Plato and Aristotle, metaphysics is not viewed as something entirely invented and separate from reason and science, but rather as the highest level and perfection of science: reason separated from the lower-order world of physicality and objects. Both philosophers mistakenly believed in a mind-body dichotomy, and as a result viewed metaphysics as the science of the "mind" or higher-level intellectual sphere. Their treatises on metaphysics can therefore be viewed as attempts to organize their theories about this metaphysical realm and its relation to reality into a coherent, consistent system. While no one has ultimately been able to provide evidence for the existence of this metaphysical realm, when taken as a metaphor for thought and knowledge, both Aristotle's and Plato's metaphysical systems provide useful insights into the subjective human experience of reality.

Plato's Divided Line and Levels of Reality

Arguably the most well-known of Plato's thought experiments is the allegory of the cave, but before reaching that concept it is helpful to discuss an idea introduced earlier in Plato's Republic: the analogy of the divided line. In this analogy, Plato attempts to describe his metaphysical system as a line divided into distinct parts, with each part representing a different level of reality. Plato, like countless other philosophers and theologians, erroneously imagines that there exists a distinction between the "mind" and the body, as if consciousness itself is somehow separable from the material processes that give rise to and sustain it — namely the brain and nervous system. As a result, he first divides his line into two unequal parts: the first representing the "visible class of objects" and the second representing "the intellectual" (Plato 231). He then subdivides each section, with the first visible section representing "illusion" and the second representing "the real objects corresponding to these images," while the intelligible half of the line is divided into reason and "the objects of the soul, as it makes its way from a hypothesis to a first principle which is not hypothetical" (Plato 231–232).

By this Plato means that the second half of the line is divided between reason and scientific inquiry on one level, and what he believes to be the essential, eternal forms that science can only reach by way of hypothesis on the other (Plato 233). As noted above, this formulation depends on the erroneous belief that one can separate the mind from physical reality — a belief with no supporting evidence and considerable refuting evidence. Setting aside Plato's fundamental error for a moment, however, one can see how the analogy of the divided line nevertheless helped Western thought develop a more accurate and productive conception of knowledge. In particular, Plato's distinction between objects and their shadows on one hand, and fundamental properties and reason's means of determining those properties on the other, helps illuminate the relationship between subjective human knowledge and reality. While Plato's notion of first principles is fundamentally flawed due to his insistence on a metaphysical sphere somehow separate from the physical, his analogy of a line with successively "higher" planes of reality is instructive. It allows one to understand, for example, the difference between a scientific theory describing a phenomenon and the phenomenon itself. In attempting to explain evolution to a skeptical audience, one could say that the theory of evolution corresponds to the first segment of the intelligible portion of the line, while the actual process of evolution corresponds to the higher level of reality, because it exists entirely independent of the theory that attempts to explain it in human terms.

The Allegory of the Cave and the Pursuit of Knowledge

Plato expands on the idea of differing levels of reality and understanding in the allegory of the cave, which posits that people are, for the most part, living in a cave watching shadows dance across a wall, and operate under the mistaken belief that those shadows are the actual objects rather than merely distorted and fragmented reflections of actual objects (Plato 235–236). Plato argues that without the "light" of philosophical inquiry, individuals will remain in the cave, ascribing meaning and importance to perceptions that are in actuality merely reflections and refractions of reality. If the analogy of the divided line is meant to demonstrate Plato's metaphysical theory in general, the allegory of the cave serves to demonstrate the social and collective importance of moving beyond the illusions of the merely visible and exploring those areas of reality and experience that require critical thought and inquiry.

Conclusion: Legacy and Limitations of Ancient Metaphysics

While both Plato and Aristotle are ultimately not very scientific, and the entire idea of metaphysics depends upon one's willingness to simply ignore the need for evidence when making claims, their investigations into the nature of knowledge and meaning are instructive because they underlie so much of Western thought, both secular and religious. Although in its original incarnation metaphysics did not mean "beyond physics" in the sense it is used today, both Plato and Aristotle depend on claims regarding a non-physical world, and as such they operate largely in the realm of the imagination rather than observable, evidential reality. Furthermore, while their belief in superstition, gods, and other non-empirical things ultimately colors their analysis to the point that much of the content is useless in any practical sense, they still managed to offer important insights into the process of human knowledge-seeking and the relationship between individual critical inquiry and the public good.