Aquinas’s First Cause Argument for the Existence of God: Preliminary Issues

Several weeks ago, I finished a lengthy trilogy of posts on an ancient argument for the existence of God known as the Prime Mover Argument (the first can be found here, the second here, and the third here). In that series, I mentioned in passing that the argument, though originating with Aristotle, was also built upon by the great St. Thomas Aquinas. Aquinas actually used five main arguments to establish the existence of God, which are called the “Five Ways.” The Prime Mover Argument, which I explained and defended in that trilogy, is the First Way. This article is the beginning of a new series, looking at the Second Way, which is known as the First Cause Argument.

Before looking at the argument itself, there are a number of preliminary issues that it is important to understand or at least note. The first is that there are many different “first cause” arguments, and Aquinas’s Second Way is just one example of such. First cause arguments, also known as cosmological arguments (not because they necessarily have anything to do with the scientific field of cosmology, but rather because they start from facts about the world or kosmos in Greek) generally seek to establish the existence of an underlying first cause of the universe, and can take a variety of approaches. For example, in my first Prime Mover Argument, I briefly discussed what I saw as the “Big Three” most popular arguments used in today’s contemporary apologetics/philosophy of religion climate, which are the Fine Tuning Argument, the Moral Argument, and the Kalam Cosmological Argument. The Kalam, as its name implies, is too a type of first cause argument, and it is by far the most common argument discussed today. It goes as such:

  1. Everything that begins to exist has a cause
  2. The universe began to exist
  3. Therefore, the universe must have a cause

The argument seeks to establish the existence of an external agent outside/independent of the physical universe, which brought into being or “caused” all of space/time/matter/energy. The Kalam argument originated with medieval Islamic thinkers, but it has reemerged due in large part to philosopher William Lane Craig’s robust use and defense of it. To see a list of some of Dr. Craig’s scholarly articles discussing the Kalam, view here. To see  possible objections to the Kalam, view here and here.

The recent appeal of the Kalam is that it makes use of the profound and startling cosmological discoveries of the past century, which seem to point to the conclusion that our universe actually “began” to exist. This, needless to say, was quite contrary to previous scientific and philosophical expectations. To be open and quite honest, I’m not sure exactly where I stand on the Kalam at the moment. I’d like to write about it more in depth in the future. But my purpose in discussing it here is to show how it relates to and differs from Aquinas’s Second Way. Both are types of first cause or cosmological arguments. Both have to do, but maybe in somewhat different senses, with things “beginning to exist.” Both have received harsh criticism and objections over the years, some of it quite poignant and thoughtful, some of it completely missing the mark. First cause arguments in general are the recipients of some extremely ill informed responses, such as the infamous “if everything requires a cause, what caused God?”

But the Kalam and Aquinas’s Second Way also have important differences. The Kalam is dependent upon the claim that the entire universe began to exist, or came into existence a finite amount of time ago. It took thousands of years of scientific development and discovery to come to a point where scientific consensus would ascribe anything like a physical “beginning” to the universe. Needless to say, this issue is still controversial and heavily debated within the fields of both cosmology and philosophy. But regardless, it is no where near “self-evident”  to any average person, without all of the relevant scientific/philosophical data, that the universe must have had a beginning. Aquinas’s First Cause Argument, however, much like his Prime Mover Argument, begins with a fact that is, or at least should be, immediately obvious and even undeniable to anyone and everyone via normal sense perception. Aquinas did not think we have to know that the entire universe began to exist in order to know that a First Cause exists; on the contrary, Aquinas famously thought that one couldn’t prove that the universe began. Rather, Aquinas put forth that one only has to know that anything is caused to know that a First Cause must exist.

Which brings me to my second preliminary note. The notion of “causation” itself is heavily contested amongst scientists and philosophers, and has been for hundreds of years. This might seem somewhat of an odd comment, considering that we invoke the terms and conceptions of “cause” and “effect” all the time, to explain and describe a numerous variety of types of events. But what exactly is causation? What does it mean for something to “cause” something else? In normal, everyday thinking, we might understand a cause to be something which “brings about” or “leads to” something else. For example, we often think of causes and effects in historical explanation. The most famous such case in history might be the assassination of Archduke Ferdinand, which is very often touted as the immediate “cause” of World War I, however simplistic that description actually is. What we mean by this is that the assassination of the Archduke led to, brought about, or resulted in the beginning of the Great War; that there is an intrinsic connection between the two. Or we might say that that event created conditions such that the war was an inevitable or necessary result. But that is on a large-scale level; and in reality, many such “causes” in history are hardly definite. There is a level of randomness and indeterminacy in historical affairs precisely because of the primacy of the human element involved. But we can think in much smaller and more definitive terms: a broken glass that shatters upon impact with the floor, a line of toppling dominos, the conception of a new fetus. Our entire world, our entire perception and understanding of reality, is based upon the idea of causation. After all, our physical senses just are instances of causation. If my seeing a certain object was not actually “caused” by light hitting the object, bouncing off, and being processed by my retinas and optic nerves, then I could hardly have any knowledge of that object’s reality.

And yet, it might surprise some readers to know, many philosophers and even scientists have had major doubts about the reality of causation. David Hume and Bertrand Russell, two of the most well known, well respected, and most important philosophers of modernity, both denied causality as regularly understood. Immanuel Kant, another of the most significant modern philosophers, likewise raised ardent objections to the success of first cause arguments, although he may not have rejected causality in general. As philosopher Edward Feser points out, according to Hume cause and effect are “entirely loose and separate” rather than “necessarily connected” (Feser, Scholastic Metaphysics page 52). An article in the Stanford Encyclopedia of Philosophy notes: “Hume attacks…the view of causation…that causation is an objective, productive, necessary relation experienced as power that holds between two things” (Reichenbach). Of course, the modern philosophers, leading up to today, were skeptical about things which no healthy, sane, normal person is or should be skeptical about. But this particular doubt and even rejection concerning the reality, objectivity, and nature of causality which seems to be inordinately present in modern and contemporary philosophers, as Feser mentions in several of his books, is surely taking things too far, even to the point of being nonsensical. For the whole magnificent edifice of science, so trumpeted by the moderns, is built upon this very notion of causation. No matter how strange and vague a notion it may seem upon reflection, it is certainly a self-evident feature of reality; even a fundamental feature thereof. Feser writes:

“skepticism about the possibility of our knowing objective causal connections between things, whether inspired by Hume or Ockham [a pre-modern philosopher], notoriously threatens…the very possibility of science” (Feser, The Last Superstition).

Empirical science just takes for granted that patterns of cause and effect are real and objective and discernible/identifiable aspects of our world. The scientific method itself presupposes such things, which just shows how deeply ingrained the notion of causality is to our common sense knowledge and understanding. Those philosophers who doubt causality would agree with the fact that causation seems obvious to us; but they would insist that our notion of such is perhaps illusional, or subjective mental processes projected onto reality. But  if we cannot support causation as real and objective, then all possibility of knowledge, reason, logic, and human functioning just breaks down; and indeed these modern philosophers are known for their notorious skepticism, but I would argue that upon denying causation even their ability to be skeptical breaks down. It would take a much longer post on its own to go into the details of the metaphysics of causation; and I will likely be doing such a post in the future. But it was necessary to clear up these issues at the start, for if we deny the existence of causality we can go no further, neither in this particular argument, nor in any scientific inquiry or even any other sort of argument at all; thus I will be taking the reality of causality as an obvious given.

Finally, a third preliminary note. The concept of a “first cause” is sometimes used in somewhat different senses, and thus becomes easily confused and misunderstood. Aquinas’s argument puts forth that the existence of a first cause follows directly and necessarily from the nature of causation itself. But as we’ve just seen, the nature of causation is quite complex and difficult to fully comprehend. It might be helpful to give at least a brief and introductory definition of a “first cause” before we flesh out the argument. Again, different arguments might have different conceptions of a first cause, but this definition is a basic one that I will be using and further extrapolating upon henceforth. This is from philosopher Michael Augros in his book Who Designed the Designer:

“I quickly found that great minds had grappled with that question [of whether there is a first cause of all visible and changeable things] for thousands of years. I discovered that although a handful had answered no or “unsure”, almost all had answered yes…Nearly all great thinkers of the past twenty five centuries have agreed that there had to be a first cause…”

“…the great thinkers who all insist there is a first cause used the expression first cause not to mean (necessarily) a cause before all other causes in time, but a cause before all others in causal power. It meant a cause of other causes that does not itself depend on any other cause. It meant, in other words, something that exists and acts all by itself, without deriving its existence or causal action from anything else. And it meant not a thing stuck in the past, but a thing existing in the present.” (Augros, 29-32).

Aquinas certainly ranks among those “great thinkers” who thought there must be a first cause. It is extremely important to notice the distinction between a cause “before all other causes in time” and a cause “before all others in causal power.” In fact, I might suggest that this very distinction makes up the whole difference between Aquinas’s First Cause Argument and the Kalam, and that is why I note it here, before actually introducing the argument itself, to make very careful pains to distinguish the two. The Kalam, on a very simplistic level, could be seen as invoking “first cause” in the temporal sense, where it is “first” because it came before all others. If the universe began to exist, and thus requires a cause, that cause is the “first” cause of the universe in that it exists before the universe and brings the universe into being. When Aquinas refers to a first cause, however, he is referring to a cause that exists here and now, and is “first” in the same sense that the Prime Mover is “prime,” in that it is the most fundamental cause/mover. This issue of temporal sequences of causation will be further addressed later on in the series.

In closing this first post, it is necessary to make one last comment about the argument as a whole. As many readers will probably come to notice, Aquinas’s Second Way is very similar to his First Way, in both structure and substance. So much so, in fact, that many critics have claimed that they are just the same argument, with only trivial differences. In my opinion, the arguments are indeed remarkably similar, but also have very significant differences, and these differences are where the true difficulties in establishing and defending the Second Way lie. For one thing, as I will further explain later on, it might seem somewhat obvious that an infinite regress of an essentially ordered causal series of movers cannot exist (see my Prime Mover articles), while it is not so obvious that an infinite regress of such a series of efficient  causes cannot exist. Aquinas himself even stated that the Prime Mover Argument was the “more manifest way” (Aquinas, 9) out of all Five. Furthermore, even among Thomistic scholars who think the Second Way actually works (I should point out at the beginning that the majority of philosophers, even theistic ones, do not think this argument works, but for reasons which I believe to be mistaken), there is some considerable disagreement about exactly how to interpret the argument, and one’s interpretation could potentially “make or break” the whole thing. In order to somewhat remedy this, I will, unlike how I approached the Prime Mover Argument, be looking directly at Aquinas’s own words from the Summa Theologica, and then offering different interpretations that I think might work.

For those who were expecting to see the actual argument in this post, my apologies. It is my intention to be as thorough and in depth in my approach to these arguments as possible, because that is what I believe truth deserves. So many of the ideas involved here are hefty and complex and needed to be understood beforehand. This argument is not simple or easy to fully grasp; but, when you really get down into the metaphysics of it all, I think it can be shown to be successful. So, having hopefully cleared away some of these preliminary issues, I will begin in my next post to lay out and explain Aquinas’s Second Way itself, the First Cause argument for the existence of God.




Sources quoted above, in the order in which the quotations appear:

Feser, Edward. Scholastic Metaphysics: A Contemporary Introduction. Piscataway: Editiones Scholasticae/Transaction Books, 2014. Print.

Reichenbach, Bruce, “Cosmological Argument”, The Stanford Encyclopedia of Philosophy (Spring 2013 Edition), Edward N. Zalta (ed.),<>.

Feser, Ed. The Last Superstition: A Refutation of the New Atheism. South Bend: St. Augustine’s Press, 2008. ebook.

Augros, Michael. Who Designed the Designer? A Rediscovered Path to God’s Existence. San Francisco: Ignatius Press, 2015. Print.

Aquinas, Thomas. Summa Theologica. 1265-1274. Trans. Fathers of the English Dominican Province. Coyote Canyon Press, 2010. ebook.




7 thoughts on “Aquinas’s First Cause Argument for the Existence of God: Preliminary Issues

  1. I love the academic feel of your blog — many blogs are informal, but I think the academic style really suits what you’ve got here. I positively adored reading this. Thanks so much for all the great information, written so poignantly and well-organized! 🙂

    Liked by 1 person

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