Plato vs. Aristotle: Key Differences in Metaphysics

Plato and Aristotle: Understanding Their Metaphysical Differences

Similarities Between Plato and Aristotle

To understand the main differences, it is first necessary to know the similarities. Both Plato and Aristotle understood that reality is constituted by two basic principles, one active and one passive, or intellectual and material. The active ingredient is, in both authors, the essence of things.

• For Plato, the active principle is Ideas. The material world is sensitive, and things are what they are because they "participate in those ideas."
• For Aristotle, the active ingredient is the form, and the passive principle is matter. Consider an equestrian statue made of cast iron. Its shape is a horse with a leader on top; the material is cast iron. The same cast iron can be anything, depending on its form.

Main Differences: Ontological Independence

That said, the main difference between the two authors lies in the degree of ontological independence granted to the active principle—that is, to Ideas, in the case of Plato, and Forms, in the case of Aristotle.

• For Plato, Ideas exist independently of the sensible world. There is a world of Ideas where they exist independently, are immaterial, eternal, and immutable. Sensible things never coincide with the Idea they participate in; rather, they are imperfect approximations.
• Aristotle does not believe that Forms can exist independently of matter (except for God). While Plato believed that the Idea of "table" exists apart from specific tables, for Aristotle, "table" exists only in union with matter. This theory is called hylomorphism (hyle = matter, morphe = form).

Problems Faced by Aristotelian Metaphysics

For Aristotle, as for Plato and the entire Greek philosophical tradition since the dawn of rational thought (logos), true knowledge must be knowledge of essences, not appearances. This means that knowledge can only be of that which is universal and permanent. What is presented as plural and changing can only be mere appearance—in the words of Plato, doxa.

Aristotle's Starting Point: Sensitive Information

However, unlike Plato, Aristotle proposes sensitive information as a starting point for knowledge: "There is nothing in our knowledge that has not previously been through our senses." Indeed, for Aristotle, what really exists are particular and concrete objects, that is, substances.

Aristotle's Twofold Problem

Of course, this epistemological and ontological position leads Aristotle to a twofold problem:

1. How to reconcile the existence of plural objects or individuals (subject to change) with knowledge, which must necessarily be of the universal? (Anticipating the answer: knowledge of particular objects will be of what is universal in them, that is, their form).
2. How can there be knowledge of specific individual objects if, being subject to permanent change or movement, they cannot be objects of knowledge? Even Parmenides realized this; and for Plato, their being is only a participatory being. (The answer will be: being in the act should not be absolute not-being, but rather not-being-in-act or being-in-potency).