The Third Man Argument: Aristotle's Critique of Forms

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  • 0:01 Plato
  • 0:55 Senses vs. Forms
  • 2:14 Aristotle's Third Man
  • 4:12 Lesson Summary
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Lesson Transcript
Instructor: Jessica Whittemore

Jessica has taught junior high history and college seminar courses. She has a master's degree in education.

This lesson will explain Aristotle's critique of Plato's theory of forms. In doing so, it will use a table to explain the concept of forms and senses. It will also explore how this relates to humankind.


There usually comes a time when a student begins to question some of the assertions of his teacher. It's just how it goes. One example of this was when a very famous Greek student used the third man argument to disprove his uber famous teacher's theory of forms. The student? Aristotle. The teacher? Plato. In today's lesson, we'll discuss this disagreement of sorts as we explore Aristotle's third man argument and how he used it to contradict Plato's theory of forms.

For starters, let's look into Plato's theory of forms. As we do this, please know these theories are rather complicated and abstract. For this reason, what we really want to grasp is that Plato believed in the theory of forms, while Aristotle refuted it with his third man argument. If we keep this in mind, we'll have half the battle won. On to Plato and his forms!

Senses vs. Forms

Plato believed that reality is made up of two different realms - senses and forms. Like you may expect, senses are the things we learn from our experience. They're what we can touch, hear, see, taste, etc…

Differing from this, forms are separate from our experience. They exist simply because they exist. Not tied to our experiences, Plato argues that forms stand apart from the physical realm. Trying to sort of bring it into our laps, we can think of forms as the fundamental nature of what really makes a being a being. They are not physical things - we can't touch, taste, or smell them; they are the essence. Admittedly, this is a bit of a brain bender. To try to illustrate it, I'll use my son.

As I've been working on this lesson, my son, Jake, has come into the room on several different occasions. When he walks into the room I can see, hear, and touch him. I can see the being that makes up my son. However, Plato would tell us there's something more real about my son than what I can grasp with my senses.

There's his intellect, his emotions, and his will that make him, him. In other words, Jake's humanness makes him human. This humanness is what Plato would call the form behind us all. It is a perfect, complete essence of what it means to be human. It's the form behind a human being.

Aristotle's Third Man

Now keeping Plato's ideas in mind, let's get to Aristotle's argument against this whole perfect form idea. Known as the third man argument, this one can also feel like a mental tongue twister. Stated very academically, the third man argument asserts that for something to be a perfect form, it must have all the attributes of the being. Therefore, since it has all the attributes of the being, it would have to BE the being and not JUST a perfect form of the being. Like I said, it's mental gymnastics so let's go back to my son.

Plato says that behind my son is a perfect and complete form of my son. This form is his humanness. I can't see it or touch it, but it is the perfect and complete form off all that makes him human.

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