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Ontological Metaphysics of Ancient Greece

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Plato and Aristotle in Athens

Plato and Aristotle in Athens

What Is Metaphysics?

Metaphysics is the branch of philosophy that deals with the precise nature of existence. The word itself is difficult to define; it originates from what we now refer to as Aristotle's Metaphysics, which was so named because it was published after his Physics. Aristotle himself never knew the term, and referred to this study simply as the "first philosophy." Specifically, metaphysics deals with such issues as cause and effect, objects and properties, causality and necessity, and being and universals.

What Is Ontology?

Ontology is the branch of metaphysics that deals with the nature of being. Specifically, ontological metaphysicians seek to answer the question, What does is mean to be? When you think about it, this question is not so easy to answer. We know intuitively that certain things exist, but how can we categorize the reasons they do? What differentiates objects that exist from those that do not?

Pre-Socratic Ontology

The earliest pre-Socratic philosophers viewed all matter as originating from a single substance. These monistic views proposed that the origin of existence may have been:

  • Water (Thales)
  • Fire (Heraclitus)
  • Air (Anaximenes)
  • Atoms (Democritus)
  • Undefinable Infinity (Anaximander)

Heraclitus is also well known for his theory of constant flux, which became popularized by the adage, "No man ever steps in the same river twice." To be as confusing as possible, Heraclitus put forth that everything always changes – but some things stay the same only by changing. That is, everything has the innate ability to change, but some beings only remain the same by changing; if something changes, then, it can be said to possess the property of being. You, for example, exist because you can (and do) change, while not-you does not exist because it cannot change (since it is not). Heraclitus’s flux theory leads in turn to the unity of opposites, the belief that being can imply both sameness and dissimilarity within the same set of objects.

Allegory of the Cave (Artwork by Jan Sanredam)

Allegory of the Cave (Artwork by Jan Sanredam)

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Plato's Forms

To resolve the distinctions between existential reality and illusion, Plato introduced the Theory of Forms, which poses that being consists of two worlds, the Sensible World (the ever-changing existence that we appear to endure in) and the Intelligible World, or World of Ideas, which consists of the eternal, intangible Forms. The only beings that actually exist are the Forms; each aspect of reality as we know is based upon a specific Form. According to Plato, the reason for your existence (whatever “you” is) is that there is a Form from which your experiences partake; not-you, on the other hand, does not exist because it is based upon the Form of non-being.

Plato explained the Forms via his well-known Allegory of the Cave, which describes a society that has lived from its inception inside a dark cave, seeing only the shadows cast from a fire behind it. These people believe that the shadows are the highest forms of reality, until one prisoner is freed and sees the fire; after suffering from the light, he will realize that the fire is more real than the shadows it caused. When he then exits the cave and views the sun, he will understand that it is the true cause of everything he sees. Analogously, humankind exists in the world it appears to understand, despite the true Forms that are the actual source, cause, and foundation of being.

Aristotle's Categories

Unsatisfied with the positions of Plato, Aristotle developed the Theory of Categories to define the highest levels of classification of existence. Everything that can be expressed as existing can be described by at least one of ten Categories. Aristotle posited that being has, in addition to its primary sense, related applicable senses. For example, as you exist, you have, in addition to your principal sense of being, the senses of your physical and emotional characteristics (each of which is a being, albeit not insofar as it itself is). All beings are related in that they refer to one central idea (though not to one object per se). Therefore, an object that does not exist is one that cannot be described by a Category.

The ten Categories (in no specific order) are:

  1. Substance
  2. Quantity
  3. Quality
  4. Relation
  5. Place
  6. Time
  7. Position
  8. State
  9. Action
  10. Affection

Aristotle further expounded upon the meaning of being by distinguishing between what he termed the subject (what a given statement is about) and the predicate (what the statement says about its subject). According to Plato, any predication refers simply to participating in a Form; that is, the statement “x is y” means that x is based on the Form y. Aristotle felt that this model was too oversimplified, as it could not differentiate between predications that are essential (e.g., “Aristotle is a human”) and those that are accidental in nature (e.g., “Aristotle is intelligent”).

The Categories



That which cannot be predicated



How much

Five cubits


Nature of an object



Comparison labels




In Athens








Physically having



Result of a change



Passively undergoing

Is chopped

Further Reading

The best way to gain a clearer understanding of discussed concepts is to read the original sources. For a basic introduction, I highly recommend the W. D. Ross translation of Aristotle's Metaphysics and Harvard University's translation of Plato's Republic, both of which are available online. Another great reference is the Stanford Encyclopedia of Philosophy.

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