For more context about Plato’s metaphysics these posts should be helpful. For Aristotle, these might provide a helpful background.

It is important to realize that Aristotle did not entirely reject Plato’s view of reality. He did, however, believe it needed improvement. In this essay, we turn to Aristotle’s view of ultimate reality and contrast it with Plato’s because that is where the biggest difference lies between the two thinkers. It is certainly the most significant difference when it comes to the development of metaphysics in Western intellectual history.

We saw in our series on Plato, that his conception of Forms¹ (or universals) were his answer to the classical problem of the one and the many. He believed that by positing universal forms he could explain the unity of the diversity we see all around us. Aristotle agreed with Plato on this point. Only by the objective essences of things, can we account for the order around us, both in nature and in morality. Further, essences account for the very possibility of knowledge about things. The difference, however, between Plato and Aristotle, rests in how the Forms or essences are related to particular things.

Early in the Metaphysics, Aristotle provides his own summary of Plato’s conceptual scheme:

…[Plato], having in his youth first become familiar with Cratylus² and with the Heraclitean doctrines (that all sensible things are ever in a state of flux and there is no knowledge about them), these views he held even in later years. Socrates, however was busying himself about ethical matters and neglecting the world of nature as a whole but seeking the universal in these ethical matters, and fixed thought for the first time on definitions; Plato accepted his teaching, but held that the problem applied not to sensible things but to entities of another kind—for this reason, that the common definition could not be a definition of any sensible thing, as they were always changing. Things of this other sort, then, he called Ideas, and sensible things, he said, were all named after these, and in virtue of a relation of these; for the many existed by participation in the Ideas that have the same name as they.³

Aristotle goes on in his Physics, Nichomachean Ethics, and Metaphysics, to critically examine Plato’s theory of Forms. Some scholars have found twenty five or more arguments against the Platonic theory in Aristotle’s works. Here, we will only focus on a few of the more important ones.

The first one, is famously known as the “third man argument.” He develops this argument in his Metaphysics and Sophistic Refutations. In this argument, Aristotle states that in order to explain the similarity between a man (1) and a second man (2) we must posit a third ideal man or form of a man, a third man. But then we must explain the similarity between the first two men and the form of a man with another, “higher” form of a man. The situation becomes an endless regression of positing further higher forms and the original instance of the first man or thing is never explained. Because the forms are not only patterns of sensible things, but of Forms themselves, nothing gets resolved.

In book two, chapter two of his Physics, Aristotle argues against the existence of separated Forms based on the mathematical properties inherent in physical objects. Here, Aristotle makes the point that physical bodies contain surfaces and volumes, lines, and points, and these are all mathematical properties. Aristotle makes the common-sense observation that material objects have mathematical properties and uses this fact to mount an interesting critique of Plato’s Forms. Remember, for Plato, forms are separate from matter. Forms exist in an ideal transcendent realm away from the realm of becoming and change. According to Plato, there are not any Forms in material objects. Aristotle finds this situation incredibly hard to believe. Plato’s theory of the Forms says that among the Forms are mathematical objects such as the form of equality, the form of a triangle, the form of a triad, and so forth. Aristotle reasons that mathematical objects can not be separated from material objects because material objects have mathematical properties. He concludes that if mathematical objects (a sample of Forms) could not be separated from material objects (physical things), then forms can not be separated from matter. Physical things have mathematical order to them.

In his Nicomachean Ethics, Aristotle makes an important ethical objection. He points out that Plato’s Form of the Good is only an ideal to to be contemplated. It does not have effective power itself. The Form of the Good is an ideal that can not effect change or transmit potency. If, on the other hand, particulars have no form in them and are only matter, what then inclines the particular towards orderliness, beauty and to its good? What is there in matter, material beings, that gives them their natural impetus and direction towards the good, if Forms are transcendent and not immanent in matter?

All these questions and objections, point to the biggest problem that Aristotle believes is at the center of Plato’s theory. It is the problem that the Forms are separated from matter and sensible things. Aristotle correctly represents Plato as having placed the ultimate causes of things (the Forms) in a transcendent world and thus separated from the things they are supposed to be the causes of. Aristotle’s great concern was to discover the cause of a thing or the cause of a property of something. He thought that by studying individual things, one could rationally discern the basic causes and principles of all Being. To understand why something is the case, we must first examine its cause.

In book one, chapter nine of his Metaphysics, Aristotle describes what he thinks is the biggest problem with Plato’s view of reality:

Above all one might discuss the question what on earth the Forms contribute to sensible things, either to those that are eternal or to those that come into being and cease to be. For they cause neither movement nor any change in them. But again they help in no wise either towards the knowledge of the other things (for they are not even the substance of these, else they would have been in them), or towards their being, if they are not in the particulars which share in them; though if they were, they might be thought to be causes, as white causes whiteness in a white object by entering into its composition …

But, further, all other things cannot come from the Forms in any of the usual senses of “from.” And to say that they are patterns and the other things share in them is to use empty words and poetical metaphors …

Again, it would seem impossible that the substance and that of which it is the substance should exist apart; how therefore, could the Ideas, being the substances of things exist apart? In the Phaedo the case is stated in this way—that the Forms are causes both of being and becoming; yet when the Forms exist, still the things that share in them do not come into being, unless there is something to originate movement.⁴

Aristotle points out that, by definition, Forms do not change because they exist in an unchangeable realm of being without becoming. The result is that Forms have no potency or ability to effect change. The separation between being and becoming, Form and matter, is very significant indeed. Platonic Forms have no way to account for the change, motion, coming into being and ceasing to be that one experiences every day.

As we have seen, Aristotle does not reject the idea of essence or Form entirely. In the next post, we will explore the most important elements of Aristotle’s metaphysics and his solution to the Platonic separation of Form and matter.

1It may not be entirely correct, but for our purposes, we’ll use “forms,” “universals,” and “essences” synonymously. The term “idea” is also used to describe the Platonic Form.

2Cratylus was a follower of Heraclitus but pushed the teaching of his master even further, for he said that one could not step into the same river even once!

3Aristotle, Metaphysics, 987a-b, tr. W. D. Ross, in Basic Works of Aristotle, ed. Richard McKeon (New York: Random House, 1941).

4Ibid., 991a-b.