Aristotelian Metaphysics: A Critique of Plato's Theory of Ideas

"All men by nature desire to know." With these words begins the first book of Aristotle's Metaphysics. That desire to know culminates in the acquisition of wisdom, which is, for Aristotle, knowledge of the causes and principles of being. And that knowledge is the object of metaphysics, the science of first causes and principles of being, the knowledge of self "as being," knowledge of the ultimate cause of nature and reality.

Aristotle's Reaction to Plato's Theory of Ideas

Aristotelian metaphysics is developed largely in reaction to the theory of Ideas of Plato. Aristotle does not appear to have any opposition to or criticism of the theory of Ideas while in the Academy. It shows, on the contrary, that the first criticisms of the theory of Ideas are developed after his abandonment of the Academy, where Aristotle begins to shape his own philosophy. We must remember, however, that Plato had already criticized the theory of Ideas in the Parmenides, and probably the theory of Ideas was the subject of much controversy at the Academy. It makes no sense, therefore, to look at the Aristotelian critique of the theory of Ideas as a reason for any personnel issues that may have faced Aristotle with Plato, but, as Aristotle himself says in the "Metaphysics", the mere pursuit of truth.

The Universal and the Problem of Subsistence

Aristotle would agree with Plato that there is a common element among all objects of the same class, the universal, the Idea, which causes us to apply the same label to all objects of that type. He allowed, therefore, that the universal is real, but not having an independent existence of things, i.e., it is not subsistent. The theory of Ideas, moreover, by giving reality to the universal, the Idea, doubles for no reason the world of visible things, establishing a parallel world that in turn would require explanation.

The Problem of Movement and Change

Nor is it able to explain the movement of things, which was one of the reasons for its formulation. Remember that, like the pluralists attempted to explain with his proposal permanence and change, the theory of Ideas is proposed for the same purpose. However, this theory does not offer any evidence to explain the movement, the change. As being immobile and unchanging, if things are an imitation of the Ideas, they would also be immobile and unchanging. But if they change, where does that change come from? ("Metaphysics", Book 1.7).

The Separation of Substance and Essence

Aristotle considers the theory of Ideas is impossible since it provides a separation between the visible and the intelligible world, i.e., between the substance and that which, therefore, is a substance's form or essence. Ideas, in effect, represent the essence of things, i.e., that by which things are what they are. How is it possible that that by which something is what it is, is not residing in the object but outside it? How is it possible that what makes the man is a man, his essence, the Idea of man, not residing in the male, but that exists independently of him? Plato's formulations to try to explain the relationship between Ideas and things, theories of participation and imitation, moreover, far from explaining the relationship, are just metaphors.

Similarly, it posits the way to explain the similarity of concrete objects. In this mode, we would be chained to infinity, requiring a model of the model, which would lead us to the absurd. On the other hand, things cannot come from Ideas, but the first is a crucial assertion of the theory of Ideas. The Ideas cannot be the cause of things, yet the same Plato explains in the Timaeus that Ideas are only the model on which the Demiurge inspires things, that is, they are the exemplary causes of things, not their efficient causes. ("Metaphysics", Book 1.7).

Aristotle's Own Metaphysical Foundations

In the Aristotelian critique of the theory of Ideas, we can envision the foundations of his own metaphysics: against the impossibility of Ideas to explain the real cause of what is, he proposes the theory of the four causes. And against the irrationality of Ideas, he proposes his theory of substance. The inconsistency of the Platonic explanation of change will lead him to propose the distinction of being in act and being in potency. Aristotle does not suppress the gulf, but introduces it into the interior of the same (sublunary) things, leaving the supralunar world safe: a celestial region absolutely ordered, ethereal, and regular.