Causality: What are the Four Causes of Things?
One of the first things we learn about something is its name. We see this principle in toddlers who spend much of their time grappling with the names of things, whether they are dogs and cats, trucks and ponies, or Mom and Dad.
At some point, the simple task of identification is not enough to satisfy the child and parents start to face the dreaded question, “why?” This shift mirrors a shift in our own engagement with the world as we seek to understand it more deeply by turning from the mere fact of things to an understanding of their causes. Of course, the question “why?” can be asked and answered in a myriad of ways and it is worth taking a moment to probe its depth.
Take, for example, 8-year-old Junior approaching his loving Daddy, source of all knowledge and wisdom in his little world, and asking, “Why is the sky blue?” Dad might try to get off easy and simply answer, “Because the sun is out.” Although even a child knows that the sky is only blue during the day, Dad’s statement expresses an important point. The sky is not always blue, and the reason it is blue in the day but not at night is because of the sun. By its agency, as an intense source of light, the sun causes an effect in the sky that lights it up and makes it appear blue. The sun is an efficient or agent cause of the sky’s blue color.
Unfortunately, Junior is not going to let Dad off that easy and persists asking, “Why is the sky blue during the day?” Realizing he’s not getting off so easy, Dad replies, “Because the sky absorbs a lot of the light from the sun, and some of that gets showered down on us.” This second reply touches on what is known as “final causality,” focusing on the natural tendency of the air. Analogous to the way we can explain our actions by referring to the goal or end we intend, we can explain many natural processes as a tendency towards a state of stability and rest. As the light from the sun excites the air and is absorbed, the air releases this extra energy to return, momentarily, to its relaxed state and some of that energy reaches us as light, the brightness of the sky. Once the sun goes down the air is able to simply relax in its natural rest state.
Undeterred, Junior presses on with a simple, “Why?” Dad, seeing that things are getting serious, answers, “Because the sky is a big layer of air with lots of little parts, little particles of air. Any particular piece of sunlight might hit any particular piece of air and send it off in a random direction, some of it coming towards us.”
By appealing to the structure of the sky, as a diffuse gas, and the properties that follow from that structure Dad has laid out an argument from form. Broadly speaking, a formal cause describes the shape or organization of something and all the various activities that follow from it. While the form of air may simply be the arrangement of molecules, in some things, like living organisms, the form describes not only for the arrangement of parts, its molecules, cells, and organs, but also the ordering of those parts to the good of the whole organism, and the activity of the organism as a whole.
Rather enjoying the worried look on Dad’s face, Junior again replies with a further query, “Why is the sky blue?” Not willing to give up, Dad presses on, “Because the molecules of the various gases that air is composed of are much smaller than the wavelength of visible light, the shorter wavelength blue light is scattered much more frequently.”
Here we have an argument from what air is made of, its matter. While the organization and activity of something is ultimately determined by its formal cause, the matter, or material cause, limits the potential forms the thing can take on. The density and temperature of air can be changed creating various weather patterns, but no natural process can force a bunch of air molecules to take on the form of a hippopotamus, however delightful that would be to Junior.
It may seem that Dad has made a valiant effort at explaining why the sky is blue to his son, providing a robust explanation from a scientific perspective and even touching on all the various senses in which the question “why?” can be answered. Junior, of course, may not be satisfied and has had the upper hand in this exchange, being limited only by his stamina and his attention span.
Note that Dad still has a wealth of causal explanations available as he can dive deeper into each of the four types of causes he touched on briefly, efficient, final, formal and material. He could turn back to efficient causality in order to trace the chain of causes that explain where the photons emitted by the sun come from or the various sources of the air in the atmosphere.
Alternatively, Dad could peel back the layers of material and of formal causality in the air. He could describe the structure and distribution of the various molecules that make up air, even delving into what the individual molecules are made of, digging down to the most fundamental structure of all matter. In the realm of final causality, Dad could place the basic scattering process of air in the atmosphere into the wider picture of order in nature, and its role in protecting the surface of the earth from more harmful radiation, regulating the air temperature, and producing the weather and climate that allow for higher levels of order and structure that we see in the ecosystem.
As we leave Junior and Dad to probe the depth of scientific understanding of the beautiful blue sky, and perhaps even some deeper philosophical truth, it is worth making a few more general comments on the idea of causality.
First the idea of the four causes, formal, material, efficient and final, dates back to the ancient Greek philosopher Aristotle (384 B.C. – 322 B.C.) and is the broad structure in which St. Thomas Aquinas approaches explanations in nature. For them a cause is an explanation for how a thing comes into being, how it remains in being, and eventually, how it ceases to be, by becoming something else.1 This classical understanding of causality, where causes explain the being of things, is not the structure with which modern science generally approaches its work, but it is not contrary to modern finding and methods and any fully satisfying scientific explanation will touch on all four classical causes.
Much has been written and discussed on the role of these four types of causes over the past twenty-three centuries since they were first posited by Aristotle, and our somewhat simple example of the blue sky is far from a complete or satisfactory treatment of the topic. Nevertheless, it reveals the great value in thinking about the world in these causal categories, in particular when they are seen in the proper depth that our example tries to draw out.
Two of these causes, efficient and final, deserve a closer look because of their importance for the disputed questions that follow.
First, in efficient causality it is often possible to point to one particular cause that is the immediate agent through which the effect is made real. However, we can (and often!) ask about the cause of the agent who is itself a cause. Sometimes, this is a matter of going back in time through a chain of events, as we when trace the efficient causality of sunlight back to the sun or back to the nuclear fusion events at the sun’s core.
Other times we can see that the immediate agent is directly moved and powered by a moving agent, as when a saw cuts wood because it is moved by my hand. In this second case we find an example of instrumental causality where something acts as a cause, but only because it is empowered to act as such by another higher cause. In our example, the saw is an instrumental cause because it only acts, cuts wood, while being moved to do so by me.
Second, in our example of the blue sky, the final causality Dad describes is fairly simple: It involves the return of an excited molecule to its stable rest state. While this aspect of stability is the basis and root of final causality, we can see even more clearly a sense of order that arises from it in more complicated things. In living things in particular we see a tendency not towards any state, but towards states of perfection. An acorn tends to become a full grown mature oak, a stable state capable of producing more acorns and oaks. A puppy tends to become a full grown mature dog which in turn can produce more puppies and dogs.
We can see an even higher aspect of final causality in ourselves, when we consider the ordering principle of our own actions. We act with particular goals in mind, which are particular stable states in ourselves and in the world, which we think will make us happy. We look at the world and try to change it in little ways to be better for us. This aspect of final causality grounds the world of ethics and morality, which is rooted in the basic idea of tending toward a stable and perfective state.
Sometimes when people hear the phrase final causality, which is sometimes called teleology, they assume that it refers to the highest form of final causality, the imposition of an external will on things. To many it seems like this is contrary to the very goal of our study of nature, the study of the inner working of the world around us. If teleology is only viewed as the external imposition of an intelligent will, they are right that it is contrary to this study.
However, at its root, teleology begins with the basic internal tendency of things to move towards particular stable states by their nature. Indeed, if it were not for this basic internal tendency of natural things to move towards stability, the whole project of science would be impossible because there would be no consistency or order to make nature intelligible.
— Bro. Thomas Davenport, O.P.
St. Thomas Aquinas De Principiis Naturae, 18. ↩