I have explained how substances and explanation are connected in a previous post. I mentioned that there are four ways to understand substances: materially, essentially, causally and teleologically. In a different post, I mentioned that change needs to be explained by the use of powers. These ideas belong together. Each change has a purpose, a passive object and an active subject. Each change is the result of a power which belongs to a substance, has a purpose and is usually activated by another power.
I have already shown that every change has a passive object and an active subject. To show that every change also has a purpose is simply to show that every change must have a purpose in order to exist at all. When something changes, the passive object is what is being changed and the active subject is what changes it. An explanation for the change is found by considering the subject rather than the object. Since the subject changed a particular object, it must have been pointed at that object. If it pointed somewhere else, then it would have changed something else instead. If it were not pointed at anything, then nothing at all would be changed.
Change always happens because of a power. This is true by definition. So if change always has a purpose, then powers always have purposes as well. Since changes are always caused by things, it follows that powers belong to things as well. Therefore, the only remaining thing to prove is that powers are usually activated by another power.
When we have a change that happens, there are several ways to ask why that change occurs. Let’s consider the example of freezing water. We can ask why water freezes (the teleological question). If we do that, then we must consider the higher causes in water. We can also ask what caused the water to freeze. This is seeking a causal answer. The teleological answer is that positive and negative charges of water molecules and the loss of energy that causes them to become a solid crystalline structure. The causal answer is that heat energy is removed from the water by the cold air (perhaps in a refrigerator). Each of these answers can be questioned in both of these ways as well. The water freezes because it is caused to freeze by the cold air. One of these powers activating is what causes another power to activate. In higher causes this is true as well: the molecular structure of water is continually causes the water to be capable of being frozen at 0 degrees C.
When we consider the most specific category that a thing belongs to, there will be some powers that the thing has because it is that kind of thing. For example, human being is a most specific category. Humans are different from other primates because they are rational. Therefore, the highest powers in human beings will be rationality. The purpose of rationality will also be the purpose of human beings as a whole.