Aristotle’s Theory of Change

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How Objects Change

One of the biggest problems that ancient Greek philosophers dealt with was the problem of change. Why and how do objects change? Plato had agreed with a number of Greek philosophers before him that change was an uncomfortable dilemma. Their reasoning was that Truth was something that was perfect, and perfection is unchanging. Perfect circles are always perfectly circular. Anything that changed was not perfect. Plato’s Forms address this—they are perfect and unchanging, and they are what are fully real; the objects that change in the visible realm are less real. Another problem these philosophers had was that change seemed to them to be a movement from nonbeing to being, something being created out of nothing, which was nonsensical. For example, it appears to our senses that an acorn stops being an acorn and an oak tree starts to exist. Some questioned how this can be, that an object of one kind can disappear and another appear. Parmenides went so far as to seem to declare that all appearances of change were illusions. (This is what happens when reasoning is allowed to run free without grounding in experience.)

Aristotle accepted that objects change. This is consistent with his view that physical objects are fully real and are the only things that fully exist. Change occurs to real things; thus, change is real. We still need an explanation of how objects change. How do acorns seem to disappear and oak trees appear? How does an oak tree have leaves in the summer but not in the winter? Plato’s Forms are powerless to explain changes in objects, so Aristotle needed to come up with an explanation. His theory is ingenious. He combines several concepts into an account of change that significantly influenced the medieval and early modern world. The concepts he used are form and matter, potential and actuality, and the four causes. We’ll discuss each in turn.


Form and Matter

First, let’s look at what Aristotle means by form and matter. What Aristotle means by “form” is not at all what Plato means by “Form.” We’ll capitalize Plato’s Form but not Aristotle’s form because Aristotle does not see the form of an object as being a higher archetype. It is simply something in objects in the world. Aristotle’s form is the answer to the question, “What is it?” It is the answer to what constitutes an object’s essence or “whatness.” What is it? It’s a tree. But what is a tree? A tree is defined by a distinct set of qualities that make it a tree and not something else. This set of qualities is its form. It’s perhaps easier to see when we talk about a human-made object like a drinking glass. It’s form is cylindrical, about seven centimeters in diameter and twelve centimeters tall; with a solid, closed bottom; and an open top, that is used to drink beverages.

Every object has a form, its “whatness,” but, Aristotle says, every object is also made of matter, its “thisness.” The drinking glass is made of matter, specifically glass, and more specifically, this particular hunk of glass. I can hold it and say “this is made of glass,” indicating its “thisness.” Another object may have some of these qualities, the same shape, perhaps, but if that object’s matter was something flimsy or soluble, it can’t be used as a drinking glass. It still has a “thisness,” but its “whatness” is not the form and essence of a drinking glass.

It’s important to remember that for Aristotle, matter is nothing in and of itself. Matter is pure potential but devoid of actuality (we’ll talk more about that next). Matter is amorphous and characterless, devoid of form, and only becomes an object when form takes hold of it to create a substance. This is true even though we do not find any matter that has not been formed. Matter in an object can be formed into a new object. In the case of a statue, the sculptor takes matter and changes its form from a hunk of marble into a finished statue. For an oak tree, the matter is changed from the form of an acorn into the form of an oak tree. The oak tree doesn’t come from nonbeing into being; it is an acorn that changes form into an oak tree.

Form and matter are the two ingredients of objects, but we still need to know how they change. The next concept is the spectrum of potentiality and actuality.


Potentiality and Actuality

Change, for Aristotle is a matter of potentiality and actuality. All objects that we perceive in the world have potentiality and actuality. Objects all have actuality because we can perceive them; if they didn’t have actuality, then they wouldn’t exist for us to perceive them. But every object also has potentiality—the potential to become something more or something else—the potential to change. We only find things that have been actualized into what they are now. They are actualized but also contain the potential to actualize into something else. Only a perfect supreme being with perfect actuality could have no further potential. All the objects we experience are a combination of actual and potential.

Consider an acorn. If I held one up to you and asked you what it is, you’d reply, “It’s an acorn.” Having had enough experience, you can identify the “whatness” of the object as an acorn. If I then ask you what an acorn does, you’d say that acorns grow into oak trees; an acorn is the seed of an oak tree. Okay. Now I ask you, what is it in the acorn that tells you it is going to be an oak tree? Just looking at the acorn, you can’t tell that. If you sliced an acorn open you aren’t going to find a tiny oak tree hiding inside just waiting to burst out. Today we can analyze the DNA of an acorn and match it to the DNA of grown oak trees, and thus we can say an acorn can grow into an oak tree because of its genetic makeup. Obviously, though, Aristotle and everyone else in his time didn’t have access to DNA information. So how did he explain how acorns changed into oak trees? And what’s more, acorns don’t turn into anything else. They don’t turn into maple trees. They don’t turn into cabbages. They don’t turn into beavers. Acorns only change into oak trees. How does Aristotle explain that?

Aristotle explains it by saying that every object has a certain potentiality that determines what that object is capable of becoming. An acorn only possesses the potential to become an oak tree. It has no potential to become a maple tree, cabbage, or beaver. Every kind of object has a limited set of potentiality within it, and that’s part of the essence of objects. Aristotle’s explanation has the same result as our DNA explanation, and you have to give credit to Aristotle for devising an explanation that, based on the information he had to work with, is rather accurate.

Continuing to consider our acorn, the acorn has the potential to become an oak tree, but it can only actualize that potential under certain circumstances. For years, when I’ve taught this course in person, I’ve carried in my backpack an acorn, using its potential as a prop for this very philosophy lesson. Clever, huh? Anyway, all the years that this acorn has been in my backpack it has never changed into an oak tree. That acorn still, after all these years, has the potential to become an oak tree, but it’s never been able to actualize that potential because some jerk has been carrying it around in his backpack. If instead, that selfish philosophy professor had put the acorn in the ground, given it some water, and let it get some air and sunlight, it could have actualized its potential to become an oak tree. Interestingly, Aristotle seems to imply that an object not only has a certain set of potentials but also the desire to actualize those potentials. Medieval philosophers later picked up on that. Whether or not Aristotle believed that an acorn wants to change into an oak tree, we can understand it and every other object as being along a spectrum of potentiality and actuality. But, however much potential an object has, that potential must be actualized. Something has to happen to it.

The Four Causes

Aristotle explains how something’s potential is actualized with the Four Causes. To understand change in the world, we need to understand that causes affect objects. By “cause,” Aristotle meant something different than how we use the word today. Today we mean “cause” strictly in a mechanical sense—what prior event brought about this result. Aristotle used “cause” as the answer to “why” objects are the way they are. So, although we think of a cause as being prior to an effect, Aristotle’s thinking is broader. A cause in the Aristotelean sense is a reason why something is the way it is.

Aristotle identifies four different causes, four different aspects that explain objects and change: material cause, formal cause, efficient cause, and final cause. The first cause is the material cause, which is exactly what it sounds like: What is the matter of which an object is composed? An acorn is composed of organic plant matter. A marble statue is made of marble. A person is made of organic animal matter. A wooden table is made of wood. Simple. The second cause of any object is its formal cause. This relates to the form of an object, as discussed earlier. The form and matter describe the object as it currently is. An acorn is a hunk of plant matter in the form of an acorn. An oak tree is a hunk of plant mater in the form of an oak tree. A marble statue of Zeus is marble matter in the form of what it is a statue of—a representation of Zeus.

The third cause is the efficient cause. With this cause, Aristotle is describing the effects that have affected an object. There are many processes in the world that are going on constantly. These processes affect various objects in various ways. We can understand why an object has its current form by understanding what efficient causes have affected that object. This is best understood in objects made by humans. A marble statue of Zeus has the efficient cause of the sculptor who sculpted the marble matter into the form of a representation of Zeus. That sculptor and the act of sculpting are the efficient cause of that statue of Zeus. In terms of efficient causes, it’s easy to see how the sculptor creates a statue, but how does the acorn change into an oak tree? For the acorn, the efficient causes are the soil, water, and sun that actualize the acorn’s potential. Every acorn has the potential to change into an oak tree but can only reach that potential when the efficient causes operate on it. Same with a block of marble and every other object.

Efficient causes are related to actuality in that every object has its current form because prior causes have affected it, changing it into its current form. An efficient cause can only affect objects that have the potential to be actualized by that cause. For example, fire can be an efficient cause, but it will effect change only on objects that have the potential to be affected by fire. Fire burns a candle but not a metal fork, for instance. The various processes present in the world effect change, with certain efficient causes interacting with certain objects and actualizing certain potentials in them.

Aristotle’s fourth cause is the final cause. The efficient causes that affect objects go hand in hand with an object’s final cause. This cause is final in the sense of destination. What is the end or purpose for any object? What is the function that it is meant to fill? In Aristotle’s writings, there is a strong sense that everything has a purpose, that everything is working toward its own end or goal. The final cause is an object’s goal and purpose. An acorn’s final cause is to become an oak tree. This is that idea I touched on earlier that an object desires to actualize its potential. Whether it actively desires it or not, there is, in Aristotle’s system, only one reason why an acorn exists: to become an oak tree. Acorns either fail in that purpose, or they succeed in that purpose. In the natural world, every seed and every baby animal has the final cause of growing up to become the organism it is meant to be. When we look at human-made objects, the same principle applies. What is the purpose of a statue of Zeus? To be present in a temple dedicated to him. That purpose is why the sculptor sculpted the statue and why every other human decision was made about the statue. Why did the sculptor choose Zeus? Why choose marble? Why hire a sculptor in the first place? All of these questions are answered by the final cause of the statue. The final cause is inherent in the object’s essence or form. Essential to being an acorn is the purpose of becoming an oak tree.

In Aristotle’s view of the world, everything is working toward its final goal and purpose. Acorns become oak trees, baby beavers become full-grown beavers, blocks of marble becomes statues, wood becomes tables, and so on. Everything is moving toward a purpose. If the efficient cause is there, then the potential that is related to the final cause is actualized and the purpose is fulfilled. Using Aristotle’s Four Causes, we explain an object by answering four questions about it: what it is made of, what made it the form it is, what or who produced it, and what its purpose is.

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