Second Way: The Argument from Efficient CausationBefore we began the First Way, we needed to introduce the concepts of Act, Potency, and Motion. As we proceed to the next four demonstrations of God’s existence, we will need to become familiar with the idea of a cause. Just as in the case of “motion”, the word “cause” has a common-sense meaning which lacks the precision of the philosophical meaning given to the term by St. Thomas. The nature and distinction of various kinds of causes is essential for the ability to understand Thomistic thought, and each of the latter four arguments for God’s existence corresponds in some way to one of the four kinds of causes described below. Therefore the reader is advised to pay close attention to this section.
Causation and Kinds of CausesImagine the following scenario. You receive a call from a friend, who wants to show you his stylish new haircut. The friend arrives and you discover that he has somehow transformed his scalp into a map of the Western Hemisphere: the closely cropped hair represents landmasses, and the bald patches represent bodies of water. He proudly displays the haircut to you, and in your shock all you manage to say is “Why is your head like that?” This general question “Why” could be interpreted by your friend in a variety of different ways, and he can answer differently depending on how he interprets it.
In the first place, the question might be looking for the purpose or intention governing the haircut. Why did you choose to do this? What were you trying to accomplish? What was your goal in cutting your hair this way? In this case, the proper answer might be: “I did it so I would always have a map with me.” Second, the question might be looking for the source of the haircut. Where did this new scalp design originate? Who made his head look like that? The answer might be: “My barber did it for me. He suggested the idea.” Third, the question might be seeking an explanation of the pattern. Perhaps you did not realize that the hairstyle is a map, and therefore need to be told what it is, or what constituent bald and hair patches form as a whole. The answer would be: “It is a map of the western hemisphere!” Fourth, you might not have realized what the map is made of. Maybe you cannot tell that the light patches are your friend’s freckled skin, and the dark bits are hair (rather than paint, or a tattoo). In this case you might be asking what kind of stuff the scalp-map is made up of. The answer would be: “It’s made up of bald patches and short haired patches.”
Each of these four questions gets at the “Why?” of the haircut in a different way, and each answer gives a different sort of explanation of the thing: its purpose, its origin, its essence, or its component parts. In Aristotle’s philosophy, these four kinds of explanations are called the “Four Causes”. The English word “cause” is the translation of the Latin “causa”, which is itself a translation of Aristotle’s word αἰτία, which means “reason or explanation”. When we understand the reasons or causes of a thing, we have grasped all the important aspects of it: where it came from, what it is tending toward, what it is made up of, and what it is in itself. Since it is useful to be precise about how we are analyzing things when we perform scientific investigations of them, we assign each kind of explanation a technical name:
The final cause is the answer to the question “What is this thing’s purpose or aim?” When we understand a thing’s final cause, we understand the end-goal or stopping point of its motion, or the intention of the person directing it. “Final” comes from the Latin finis, meaning “end”. Often when speaking of a thing’s final cause, we will simply refer to its “end”.
The efficient cause is the answer to the question “What made this thing come into being?” The efficient cause is the agent which put something into its present condition, or which gave it its existence altogether. “Efficient” comes from the Latin efficere, meaning “to bring about or make”. Oftentimes we refer to a thing’s efficient cause simply as its “cause”.
The formal cause is the answer to the question “What is it?” When we understand a thing’s formal cause, have grasped its nature or essence—the kind of thing it is, or the characteristic actuality of the thing that makes it whatever it is. “Formal” comes from the Latin forma, which translates the Greek εἶδος, meaning “form, shape, or kind”, the idea being that the “form” of a thing is what unites it, similar to the way the shape of a physical object unites its compenents into a whole with a definite organization and identity. We often refer to a thing’s formal cause as its “form”.
The material cause is the answer to the question “What is it made of?” The material cause tells us what kind of stuff makes up a thing, what would remain if we removed the form of the whole, or what the components of the thing would be, if we tried to make one from scratch. “Material” comes from the Latin materia, which translates the Greek ὕλη, which means “timber”, the idea being that the material cause of a thing is its component parts, just like the lumber one takes to make furniture. We often refer to a thing’s material cause as its “matter”.
In order to guarantee that the reader understands these concepts before proceeding, we will now give two detailed case studies, analyzing the four causes for each. One of our cases will analyze a natural object, in which the formal and final causes are intrinsic and not merely ascribed to it; in the other case we will look at an artifact, something which is passively made by an intentional agent, and has an extrinsically ascribed nature and finality which do not inhere in it directly.
First Case Study: Maple Tree (A Natural Object)Final Cause: The final cause of a maple tree is wherever its natural motion as a maple tree naturally tends to terminate. This can be looked at in two ways. Trivially, the end of every maple tree’s life is death. However, the death of a maple tree comes about through the removal of its vitality, i.e., what makes it a maple tree. This is not the end-point of its actualization, but of the removal of its act as a maple tree. In a second and more proper sense, the final cause of the maple tree is that stage of its life at which all of the natural potencies it has as a maple tree have been actualized—in other words, when the maple tree becomes everything a maple tree can be, insofar as it is a maple tree. This finality is reached when the tree reaches healthy adulthood and is exercising all of its natural capacities: nourishment, self-repair, growth, and reproduction. Once a maple tree reaches this stage of its life, we say that it is mature or full-grown. It has achieved its end.
Efficient Cause: The efficient cause of a maple tree is the source of its being: whatever causes this maple tree to come to be. Different aspects of a maple tree have different efficient causes. For example, the nourishment of the tree depends on sunlight, water, and nutrients from the soil, which cause it to grow. So these things might be called efficient causes of the maple tree’s growth. However, the maple tree as a whole originated in a seed, and this seed was produced by a maple tree, possibly with the assistance of pollen from another tree. Thus for the maple tree as a whole, the efficient cause is the tree or trees which generated the seed it grew from.
Formal Cause: The formal cause of a maple tree is its characteristic act: the essence of the tree, whatever about it makes it the sort of thing that it is. Because a maple tree is an extremely complex living thing, it is very hard for us to grasp the act by which it, as a whole, is one organized entity. Consequently, when we speak of a maple tree’s essence, we usually do our best to identify what kind of thing it is in general, and what the distinctive features of the thing are. In modern biology, we specify a thing’s essence in one of two ways: by giving its place in a taxonomy, or by referring to its DNA. If we give a taxonomy, we usually distinguish between the tree’s closest biological relatives by naming a unique differentiating feature—for example, its leaf shape or the structure of its branches. If we talk about its DNA, we are thinking of DNA as the biochemical component of the tree that regulates its development, and therefore leads to the emergence of its overall structure and characteristics. However, it is important to remember that neither the unique parts of the tree (e.g. its distinctive leaves) nor its DNA make up the essence or form of the tree as a whole. One could clip some leaves off of a Red Maple, or collect a DNA sample, and one would not have a tree. The essence of a tree is in its act as a whole, living thing, and is inseparable (except in thought) from any particular concrete tree.
Material Cause: The material cause of a maple tree is the stuff it is made up of. This is the easiest of the four causes for the modern reader to understand, because modern science teaches us to focus primarily on material causes. Maple trees are made up of trunks, branches, stems, and leaves. These in turn are made up of various organs and tissues, which are made up of cells, cellular components, molecules, atoms, and so on. Notice that the material cause of the tree is not sufficient to tell us the essence of the tree. One could chop down a tree and run it through a woodchipper and have all the same material components there, but what existed in the pile of woodchips would not be a tree. The material cause is what is actualized by the form or essence of the tree as a whole, living thing. A bit of wood has a certain actuality and exhibits certain behaviors, but on its own it cannot perform the act which is elicited from it when it is integrated into the whole which makes up a tree. It cannot convey nutrients, or support a branch, etc.
Second Case Study: Sledgehammer (An Artifact)Final Cause: With things that are not alive, but which come into being passively as merely the artifacts of a living thing, it is more difficult to ascribe a final cause to the thing in itself. This is because manufactured objects do not have natural essences as such: their nature in themselves is the nature of whatever they are made of, and when left to themselves they will do merely the sorts of things dictated by the natural tendencies of their parts, which is usually just to sit idly and passively decay. However, as something made, things that are intentionally produced are directed in their production and use toward some goal, which is intended by the one who made them. Thus in the case of a sledgehammer as a sledgehammer, its final cause is to perform the function intended by the one who made the sledgehammer, or the one who is employing the thing as a sledgehammer. Since sledgehammers as sledgehammers exist for the sake of smashing things, the final cause of the sledgehammer is to be actually used to smash things. If one decided to re-dedicate the sledgehammer to some other use—for example, as a doorstop—then insofar as it was intended for that new purpose, it would become a new sort of thing, and take on a new final cause.
Efficient Cause: The efficient cause of an artifact is the person who made it. Thus, the sledgehammer’s efficient cause is the manufacturer, and specifically all the people and machines that went about forming the wood and steel into a hammer. Because sledgehammers are artifacts (i.e., things intentionally designed and made), it is intuitively easy for us to grasp their efficient cause. After all, the name of the efficient cause is usually printed on the hammer itself.
Formal Cause: The formal cause of a tool is whatever about the tool makes it the sort of thing it is. Since sledgehammers have no intrinsic act that governs their development, but receive their characteristic act and identity from the way they are thought of and used by people, the formal cause or essence of a sledgehammer is inseparable from its intended use. What makes a sledgehammer a sledgehammer is the fact that it has the characteristics which lend it to being used as a sledgehammer—i.e. being swung by a person with a characteristic motion against some object. Again, if we re-purpose the sledgehammer for some other use, to some extent it takes on the essence of whatever its new function is. If the sledgehammer becomes a doorstop to the point that it ceases to be thought of as a sledgehammer, we could say that it has ceased to be a sledgehammer and has become a doorstop. The artist Marcel Duchamp famously illustrated this point by taking manufactured objects like shovels and urinals and removing them completely from their original context of use. What was manufactured as a shovel became designated, by Duchamp, as an artistic sculpture, and it therefore it lost the essence and purpose of a shovel (to remove snow or dirt, for instance) and took on the essence and purpose of an artistic sculpture (to be admired and studied).
Material Cause: Because sledgehammers are manufactured, it is easy for us to grasp their material cause, just as it was easy for us to grasp their efficient cause. The material cause of a thing is its component parts, and thus the material cause is the stuff assembled by the hammer’s manufacturer to make the final product. This includes wood, varnish, and steel. As with the maple tree discussed earlier, it is important to note that the material cause of the sledgehammer is not sufficient to give us its formal cause. If one has some wood and steel, a great number of possible objects can be made from it, for many different uses. The material cause simply tells us what goes into making a sledgehammer; it is up to its maker and user to determine what that material stuff is going to end up being as a united whole.
Now that we have explained and reviewed the four kinds of causes, we are ready to proceed to St. Thomas’s second demonstration of God’s existence, which depends on the nature of efficient causes in particular.
Different Ways of Thinking about Efficient CausesRecall from our discussion of the efficient cause of the maple tree that we can think of efficient causes in two ways: first, as the source of any particular motion or operation in a thing (e.g. the cause of the maple tree’s growth); second, as the source of its existence as a whole (i.e. the cause of there being a maple tree at all). The First Way focused on efficient causes in a looser and more general sense: the source of any particular change in a thing. The Second Way focuses instead on efficient causes in their more proper sense: the source of something’s existence as a whole.
The same distinction we made in the First Way between essentially and accidentally subordinated series of causes applies to the Second Way’s consideration of efficient causes. However, applying distinction between accidental and essential subordination to efficient causes is somewhat more difficult. In order to understand the direction of St. Thomas’s argument we must introduce a new distinction, between the nature or essence of a thing, and the individual thing as such, which we refer to as a supposit.
If you stand and point to a beautiful maple tree, rustling in the summer breeze, what you are pointing to is a maple tree, but you are also pointing specifically to that maple tree. The essence of a maple tree only exists in individual maple trees, which share the common form or nature that makes them maple trees. So what you are pointing to is not a maple tree in general, but a particular individual—this maple tree—the supposit. However, it is clear that that thing which happens to be a maple tree is distinct from maple tree-ness in general. In other words, the nature of the thing and the particular supposit in which the nature subsists are really different from each other. If lightning struck the tree and killed it, so that it was no longer a maple tree but only a fallen log, the supposit would not thereby be annihilated, nor would “maple tree-ness” in general be destroyed. There remain other maple trees, and the matter of this maple remains even though it is no longer a living tree.
On the basis of this distinction we can identify two basic ways of understanding the question “How did this thing come to be?” On one hand, there is the question of how this individual supposit came to have the form of a maple tree. In this case, the question has to do with the occasion which led to the instantiation of the general form (“maple tree”) in this particular thing.
If we pursue this question to its limits, it ends up taking us through the natural history of plant species, back to the origin of life on earth, and further, as far back as we like. We refer to this chain of occasions whereby a particular form is instantiated in a particular supposit as an accidentally subordinated chain of efficient causes.
On the other hand, there is the question of how the nature in general (“maple tree”) which is possessed by the supposit came to be. This is a question not about instantiation, but about the origins of a kind of thing. We refer to the chain of causes which bring about the existence of a kind of thing in general as an essentially subordinated chain of efficient causes. Note that whereas the first question can be answered by pointing to another maple tree, the second question cannot, because a maple tree cannot, as a maple tree, be the reason why all maple trees exist.
Furthermore, note that because the first question can be answered by another member of the same species, there is no subordination between the cause and the effect with regard to their essences: the parent tree is just as much a tree as the seed tree. Because of this, there is no reason (from logic alone) to assume that such a chain of parent trees could not have been going on for all time. For any putative first tree, we can imagine there to have been some earlier tree that gave it existence, etc., and there is no clear reason to suppose that this series could not continue indefinitely into the past.31 In other words, simply from the knowledge that this maple tree was begotten by another maple tree, we cannot logically demonstrate that there was ever a first maple tree, and not an endless series of past generations. Because this reasoning holds not just for maple trees, but for all natural kinds, St. Thomas believes that it is impossible to prove from reason alone that the world ever had a beginning.32
However, even if we grant the possibility of an unending past series of tree generations, the preceeding chain of ancestor trees will not sufficiently answer our second question, since no maple tree can explain why there are maple trees in the first place. Furthermore, because maple trees form this sort of accidentally subordinated causal series, it is clear that nothing inherently necessitates that any particular maple tree exist, since any particular tree might have never been begotten, had circumstances gone otherwise. Therefore nothing necessitates that the species as a whole should exist either. So, even supposing that there have always been maple trees, the question remains a reasonable one: Why do maple trees exist at all? This is the sort of question St. Thomas has in mind when he speaks of efficient causes in the Second Way.
An Infinite Chain of Essentially Subordinated Efficient Causes?Once we have identified the kind of essentially subordinated chain of causes St. Thomas is interested in, the argument proceeds much as the First Way did. We need to determine whether the chain of efficient causes in question could be infinite. However, it is relatively easy to show in this case that it cannot be infinite. Once we recognize that the essence of maple trees in general requires some explanation which is not a maple tree, we ask: For whatever caused the essence of maple trees in general, what caused that kind of thing to exist? Supposing that the chain goes on like this without an origin, so that every particular efficient cause owes its nature to some other higher thing, we encounter a further question: What is the reason for the existence of all of these natures in common? If every nature is caused by some other nature, then the series of natures as a whole lacks a cause, since, just as with maple trees, nothing within the series, nor the series as a whole, supplies the reason for its existence. And so, we end up with an ordered chain of dependent natures which do not ultimately have an explanation for their existence. But this is absurd. Therefore there must be a first cause.
St. Thomas explains it this way: if there is an infinite series of essentially subordinated efficient causes, each member of the chain becomes an intermediate cause. An intermediate cause communicates what is received from the prior causes in the chain to the effects which are dependent on it. But since every member of an infinite chain of causes is intermediate, the chain considered as a whole is an intermediate cause. But what is intermediate depends on what is first in order to actually cause whatever follows from it, so that if there is no first cause, there is no reason for there to be any subsequent effects. Since the efficacy of each subsequent cause is dependent on what preceded, and there is no ultimate explanation for the efficacy of the chain of causes, the chain should have no efficacy.
But if one were to reply that the chain itself is its own cause, this is absurd, since the chain is composed entirely of things that are dependent on each other for their existence, and it is repugnant to reason to suppose that a group of things, all of which are causally dependent, is, as a whole, causally independent. Therefore an infinite chain of essentially subordinated efficient causes is impossible, and there must be some cause which is itself uncaused.
Notice that this reflection reveals something: even if the universe were infinitely old, there would still have to be a first, unsubordinated efficient cause explaining why the sorts of things that exist exist. The argument does not depend on time.
Characteristics of the First Efficient CauseIf there cannot be an infinite series of essentially subordinated efficient causes, then in any such series, there must be something that is causally primary. (Note, however, that this causal primacy does not rule out the possibility of an infinite past occupied by causally dependent things.) What sort of characteristics would the first cause in such a chain have to have, in order to be first?
First, it would have a nature which was not dependent on anything of a higher nature for its existence. As a result, it could not individually have received its existence even from an another being of the same kind, since in this case we would have to ask why (since beings of this kind can exist or not exist) they exist at all. Consequently we can deduce that any first efficient cause is not only of an unmade kind of thing, but is itself individually unmade, and owes its existence to nothing beyond itself, and even, because of what it is, could not not exist. But such a thing, which causes other kinds of things, but which does not in itself come into being, and which has its own existence by nature, clearly fits the common notion of “God”. Therefore, God exists.
Notice again what we have not proven in this demonstration. We have not shown that there is only one such first cause, or that any such first cause would have to have the various attributes applied to God in Christian theology. Many of these attributes can be shown to hold of the first cause, but St. Thomas reserves them for later on. For now he is content to show that there is at least one first cause, and that its nature and existence are uncaused.
Outline of the Second WaySome natures are caused.
All essentially subordinated efficient causation must ultimately be referred to a first cause, the existence and nature of which is essentially uncaused.
A first cause, the existence and nature of which are uncaused, is what we call “God”.
Therefore God exists.