Aquinas’ First Way

St. Thomas Aquinas was quite a guy.  His most famous work is called “The Summa Theologica”, which is kind of like a systematic theology with a distinctive question and answer style.  Each question being examined has a number of articles which are given to answer it; and each article begins with a number of objections, proceeds to the presentation of an argument, and concludes with a reply to each of the objections.  

The Summais well known outside of Christianity, and is probably most famous for “The Five Ways”that Aquinas gives as proof for the existence of God.  As you would imagine, this section comes along very early in his work.  The Five Ways are given in the third article of the second question.  There is nothing, at this point, exclusively Christian about his arguments.  This is because his answers are going to be building upon one another as he goes.  His purpose at this point is only to establish that a God exists.  Once that foundation has been laid, he can move from there to determining what kinds of attributes this God must have, and eventually to formulating a fully Christian understanding of who God is.

Prior to this (in question one), Aquinas explores the nature and extent of sacred doctrine.  Determining the value and authoritative nature of sacred doctrine, he then turns to its subject matter – God, and whether or not he truly exists.  This, he covers in three articles.  

·     Whether the existence of God is self-evident. 

o  It is not self-evident, but rather needs to be demonstrated by things that are more known to us.  

·     Whether it can be demonstrated that God exists.  

o  Leaning on Romans 1:20, he determines that God’s existence can be demonstrated.  

·     Whether God exists.  

o  Since he has already determined that the existence of God can be demonstrated, this article explains how that might be done.  His answer here, as mentioned, takes the form of “The Five Ways”.

The first way is a form of cosmological argument.  But wait. Slow down.  I know what you’re thinking, but this is notan argument to say that the universe had a beginning, and thus a Beginner (that’s that Kalaam fellow).  What Aquinas presents is not an argument that depends upon chronological cause and effect relationships, but rather one that shows a hierarchy of dependencyrelationships.  First prize is not necessarily the prize given out first, but it is the most prominent and it is primarily in reference to ‘first’ that other placeholders derive their meaning.  It’s not a perfect analogy, but maybe it helps get the point across. Aquinas is not here concerned about time.  

Alright.  So, what is his argument?  In his words:

The existence of God can be proved in five ways.

The first and more manifest way is the argument from motion. It is certain, and evident to our senses, that in the world some things are in motion. Now whatever is in motion is put in motion by another, for nothing can be in motion except it is in potentiality to that towards which it is in motion; whereas a thing moves inasmuch as it is in act. For motion is nothing else than the reduction of something from potentiality to actuality. But nothing can be reduced from potentiality to actuality, except by something in a state of actuality. Thus that which is actually hot, as fire, makes wood, which is potentially hot, to be actually hot, and thereby moves and changes it. Now it is not possible that the same thing should be at once in actuality and potentiality in the same respect, but only in different respects. For what is actually hot cannot simultaneously be potentially hot; but it is simultaneously potentially cold. It is therefore impossible that in the same respect and in the same way a thing should be both mover and moved, i.e. that it should move itself. Therefore, whatever is in motion must be put in motion by another. If that by which it is put in motion be itself put in motion, then this also must needs be put in motion by another, and that by another again. But this cannot go on to infinity, because then there would be no first mover, and, consequently, no other mover; seeing that subsequent movers move only inasmuch as they are put in motion by the first mover; as the staff moves only because it is put in motion by the hand. Therefore it is necessary to arrive at a first mover, put in motion by no other; and this everyone understands to be God.

If you found that confusing, don’t worry, you’re not alone.  

First off, it’s obviously central to the argument to understand what Aquinas means by ‘motion’. To put it in his terms – motion is the actualization of a potential, which I believe is terminology borrowed from Aristotle.  He gives a couple of examples to help our understanding – wood being made hot by fire and a staff being put into motion by a hand.  These are very different things.  But we can see in each case something potential becoming actual – or in other words, we see change

To re-state his argument in the way that I understand it:

1.     Some things are in motion

a.     Aquinas doesn’t really do anything to prove this statement – he simply takes it as axiomatic.  Things are in motion.  Potentialities are actualized.  This is observable.  

2.     For potential motion to become actual motion requires actual motion.  

a.     The actual motion of the fire causes motion in the wood.  The actual motion of the hand causes motion in the staff.  If the hand only had potential motion, the staff would never move. 

3.     Things can’t be both actuality and potentiality in the same respect.  

a.     The fire in the example is already in motion – it is actually hot.  It cannot simultaneously be potentially hot, but is rather potentially cold.  (And yes, of course, there is more variance than ‘hot’ and ‘cold’, but for the sake of simplicity we’ll leave it at that).  

b.     You can almost think of there being a fixed number representing the sum total of actuality and potentiality of motion in a certain respect.  So, if the potentiality decreases (the fire warms the wood), actuality increases. The total stays constant.  

4.     Therefore, a thing cannot move itself

a.     This follows from what precedes it.  In order to produce motion, the fire has to act on something that is potentially hot – but the fire is not potentially hot, it is actually hot. Therefore a fire acting upon itself will not produce motion.  

5.     Therefore, whatever is in motion is moved by something else.  

a.     This simply follows from point 4.  If a thing is observed to be in motion, and we know that it cannot move itself, then we can understand that it must have been moved by something else.  There are no other options.  

6.     This sequence cannot extend to infinite.  

a.     If the sequence of motion extends ad infinitum, then there can be no first mover, and thus no other mover.  Now, something to bear in mind here – Aquinas is not rejecting all forms of infinite regress, but only those which form a part of causally dependent relationships. 

b.     An infinite series cannot have a beginning – because no matter how many dependency relationships you are able to identify in the sequence, there is still an infinite number remaining.  And if there is nothing to set things in motion to begin with, the thing itself would not be in a state of actual motion.  It doesn’t matter how many intermediate causes there are – for motion to occur there must be a first, non-derivative, independent cause. 

7.     Therefore, there must be a first mover.  And this we understand to be God.  

a.     All of these causally dependent relationships will eventually find their source of motion in God – who is pure actuality.  He is the first mover in every sequence and contains no potentiality.

Remember what I said about the arguments building on each other?  Ok, good.  Because all we know about ‘God’ at this point is that he is the first mover, which is hardly enough to know that he’s God.  I think this is better thought of as a retroactive designation, rather than part of the proof. Aquinas is going to spend the next few hundred pages exploring the attributes that the first mover must have. So, while it would be sufficient to the argument for him to conclude with a first mover, it is helpful for those reading the material to understand that Aquinas is going to establish a connection between the first mover and God.  

What do you think? Does Aquinas prove by this that there is a God?  Do you disagree with how I’ve interpreted his argument?  What holes do you see in it?  Did you skip to the end to see if I had any thought provoking questions? Tell me about it in the comments. 

Thanks for reading.

deacon amos martel

Rob Steele