Rationale and Thomas Aquinas

This is the third post in my series on argument mapping with Rationale. The previous posts are Argument Mapping with Rationale and More on Argument Mapping with Rationale.

To further practice argument mapping, I decided to map Thomas Aquinas’ Five Ways. These purport to be logical proofs for the existence of God. Thomas Aquinas was a theologian in the 13th century CE. Apparently, Aquinas’ writings still influence the teaching of the Catholic Church today.

Aquinas argued that the existence of God could be proved in five ways:

  1. the unmoved mover
  2. the first cause
  3. the argument from contingency
  4. the argument from degree
  5. the argument from design

I don’t propose to elaborate on these arguments in the body of the post. That’s the purpose of building an argument map. Towards the end of this article, I’ve included a copy of the Five Ways argument taken directly from Aquinas’ master work Summa Theologica (Ref. 19).

To make my position clear, I am a humanist—a member of the British Humanist Association—and atheist: as far as I’m concerned God does not exist. As this is a subject of interest, I do toddle through various relevant websites. I’d commented on one particular article and was checking out the other comments, when I spotted one typical of the bottom half of the Internet: ad hominem attacks and assertions with no evidence. Mildly (surprisingly for me) I asked for some evidence for this person’s claims and was rewarded with a presentation of the Five Ways.

I’d heard of the Five Ways before and had read a bit about them. On the face of it, I hadn’t found Aquinas’ arguments particularly convincing. They’d set my bullshit detector pinging, but I hadn’t troubled to analyse further. This seems like a good opportunity to do that.

The following diagram shows the first iteration of the map with the contention that God exists and the five supporting arguments:

Thomas Aquinas' Five Ways for proving the existence of God. Click for larger image.

Thomas Aquinas’ Five Ways for proving the existence of God. Click for larger image.

As I worked on the map, adding the details for Aquinas’ various claims and the assorted supporting claims or objections, it became clear that Rationale was rather clunky at handling wide maps. It is possible to collapse individual branches so that only a single claim box shows and the detail below is hidden. This is some help, but not perfect. In any case, with regard to the argument each of the Five Ways is a separate argument.

I’ve admitted my atheistic bias, and as I’ve worked on the maps I have tried to be as objective as possible, but one thing became clear as I searched for source material: quite a lot of people still think Aquinas is right and his arguments convincing. Many religious sources simply quote the arguments as-is. The Five Ways gleam bright with perfection; this is what they’ve been told; this is what they believe. Unsurprisingly, there are many posts pointing out the flaws in Aquinas’ arguments. I didn’t find too many sources that had convincing rebuttals of the atheist arguments. Sometimes they didn’t even bother, but resorted to ad hominem attacks—Richard Dawkins is called horrible quite a lot—or (more or less) saying “no, you’re wrong” or making some feeble appeal to authority: you can’t possibly understand Aquinas unless you understand Aristotelian philosophy. But I’m still looking, and still plan to continue to polish my maps using the guidance for defining claims discussed in the last post.

If you have a Rationale account (you can get a free one), then you can take a look at the argument map for the first of the Five Ways: the unmoved mover or the prime mover. The map is here. You can download a PDF version here.

Update 08 October 2015: A new PDF version of the prime mover map is here.

In future posts, I’ll provide argument the other four ways.

A closing quote from another atheist:

Anything that happens, happens.
Anything that, in happening, causes something else to happen, causes something else to happen.
Anything that, in happening, causes itself to happen again, happens again.
It doesn’t necessarily do it in chronological order, though.

Douglas Adams (Ref. 19)

A Note on Sources

The reference/reading list of sources used in this series of posts can be found here. Since this is a work in progress, I am posting the list separately as I anticipate additional sources being added as further posts are prepared. I have directly linked to some sources in the text, and some are noted in the map, but it was too complicated (read: too much hassle) to keep track of every source that made a similar claim that I included in my maps.

Thomas Aquinas’ Five Ways

This extract has been copied from Summa Theologica. The text of The Five Ways is available all over the Internet. I used the copy from Scribd.com (Ref. 19.).

I answer that, 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.

The second way is from the nature of the efficient cause. In the world of sense we find there is an order of efficient causes. There is no case known (neither is it, indeed, possible) in which a thing is found to be the efficient cause of itself; for so it would be prior to itself, which is impossible. Now in efficient causes it is not possible to go on to infinity, because in all efficient causes following in order, the first is the cause of the intermediate cause, and the intermediate is the cause of the ultimate cause, whether the intermediate cause be several, or one only. Now to take away the cause is to take away the effect. Therefore, if there be no first cause among efficient causes, there will be no ultimate, nor any intermediate cause. But if in efficient causes it is possible to go on to infinity, there will be no first efficient cause, neither will there be an ultimate effect, nor any intermediate efficient causes; all of which is plainly false. Therefore it is necessary to admit a first efficient cause, to which everyone gives the name of God.

The third way is taken from possibility and necessity, and runs thus. We find in nature things that are possible to be and not to be, since they are found to be generated, and to corrupt, and consequently, they are possible to be and not to be. But it is impossible for these always to exist, for that which is possible not to be at some time is not. Therefore, if everything is possible not to be, then at one time there could have been nothing in existence. Now if this were true, even now there would be nothing in existence, because that which does not exist only begins to exist by something already existing. Therefore, if at one time nothing was in existence, it would have been impossible for anything to have begun to exist; and thus even now nothing would be in existence—which is absurd. Therefore, not all beings are merely possible, but there must exist something the existence of which is necessary. But every necessary thing either has its necessity caused by another, or not. Now it is impossible to go on to infinity in necessary things which have their necessity caused by another, as has been already proved in regard to efficient causes. Therefore we cannot but postulate the existence of some being having of itself its own necessity, and not receiving it from another, but rather causing in others their necessity. This all men speak of as God.

The fourth way is taken from the gradation to be found in things. Among beings there are some more and some less good, true, noble, and the like. But ‘more’ and ‘less’ are predicated of different things, according as they resemble in their different ways something which is the maximum, as a thing is said to be hotter according as it more nearly resembles that which is hottest; so that there is something which is truest, something best, something noblest, and, consequently, something which is uttermost being; for those things that are greatest in truth are greatest in being, as it is written in Metaph. ii. Now the maximum in any genus is the cause of all in that genus; as fire, which is the maximum of heat, is the cause of all hot things. Therefore there must also be something which is to all beings the cause of their being, goodness, and every other perfection; and this we call God.

The fifth way is taken from the governance of the world. We see that things which lack intelligence, such as natural bodies, act for an end, and this is evident from their acting always, or nearly always, in the same way, so as to obtain the best result. Hence it is plain that not fortuitously, but designedly, do they achieve their end. Now whatever lacks intelligence cannot move towards an end, unless it be directed by some being endowed with knowledge and intelligence; as the arrow is shot to its mark by the archer. Therefore some intelligent being exists by whom all natural things are directed to their end; and this being we call God.

Reply Obj. 1. As Augustine says (Enchir. xi.): Since God is the highest good, He would not allow any evil to exist in His works, unless His omnipotence and goodness were such as to bring good even out of evil. This is part of the infinite goodness of God, that He should allow evil to exist, and out of it produce good.

Reply Obj. 2. Since nature works for a determinate end under the direction of a higher agent, whatever is done by nature must needs be traced back to God, as to its first cause. So also whatever is done voluntarily must also be traced back to some higher cause other than human reason or will, since these can change and fail; for all things that are changeable and capable of defect must be traced back to an immovable and self-necessary first principle, as was shown in the body of the Article.


  1. […] my last post on Rationale, I illustrated using the software to map the first of Thomas Aquinas’ Five Ways—logical […]

  2. […] Mapping with Rationale More on Argument Mapping with Rationale Rationale and Thomas Aquinas Rationale and Thomas Aquinas Part the Second If Not Rationale, […]

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