Primary sources on the topic:

Summa Theologica:

Latin

English:
Old
New

Summa contra Gentiles

Latin and English

By argument:

First way

Summa Theologica  I, Q 2, A 3 Paragraph 1:

The first and clearest way is that taken from movement or change (ex parte motus):

It is certain, and obvious to the senses, that in this world some things are moved. But everything that is moved is moved by another. For nothing is moved except insofar as it is in potentiality with respect to that actuality toward which it is moved, whereas something effects movement insofar as it is in actuality in a relevant respect. After all, to effect movement (movere) is just to lead something from potentiality into actuality. But a thing cannot be led from potentiality into actuality except through some being that is in actuality in a relevant respect; for example, something that is hot in actuality—say, a fire—makes a piece of wood, which is hot in potentiality, to be hot in actuality, and it thereby moves and alters the piece of wood. But it is impossible for something to be simultaneously in potentiality and in actuality with respect to same thing; rather, it can be in potentiality and in actuality only with respect to different things. For what is hot in actuality cannot simultaneously be hot in potentiality; rather, it is cold in potentiality. Therefore, it is impossible that something should be both mover and moved in the same way and with respect to the same thing, or, in other words, that something should move itself. Therefore, everything that is moved must be moved by another.

If, then, that by which something is moved is itself moved, then it, too, must be moved by another, and that other by still another. But this does not go on to infinity. For if it did, then there would not be any first mover and, as a result, none of the others would effect movement, either. For secondary movers effect movement only because they are being moved by a first mover, just as a stick does not effect movement except because it is being moved by a hand. Therefore, one has to arrive at some first mover that is not being moved by anything.

And this is what everyone takes to be a God.

Contra Gentiles I.13

Second way

Summa Theologica  I, Q 2, A 3 Paragraph 2:

The second way is based on the notion of an efficient cause:

We find that among sensible things there is an ordering of efficient causes, and yet we do not find—nor is it possible to find—anything that is an efficient cause of its own self. For if something were an efficient cause of itself, then it would be prior to itself—which is impossible.

But it is impossible to go on to infinity among efficient causes. For in every case of ordered efficient causes, the first is a cause of the intermediate and the intermediate is a cause of the last—and this regardless of whether the intermediate is constituted by many causes or by just one. But when a cause is removed, its effect is removed. Therefore, if there were no first among the efficient causes, then neither would there be a last or an intermediate. But if the efficient causes went on to infinity, there would not be a first efficient cause, and so there would not be a last effect or any intermediate efficient causes, either—which is obviously false. Therefore, one must posit some first efficient cause—which everyone calls a God.

Third way

Summa Theologica  I, Q 2, A 3 Paragraph 3

The third way is taken from the possible and the necessary, and it goes like this:

Certain of the things we find in the world are able to exist and able not to exist (quaedam quae sunt possibilia esse et non esse); for some things are found to be generated and corrupted and, as a result, they are able to exist and able not to exist.

But it is impossible that everything that exists should be like this; for that which is able not to exist is such that at some time it does not exist. Therefore, if everything is such that it is able not to exist, then at some time nothing existed in the world. But if this were true, then nothing would exist even now. For what does not exist begins to exist only through something that does exist; therefore, if there were no beings, then it was impossible that anything should have begun to exist, and so nothing would exist now—which is obviously false. Therefore, not all beings are able to exist [and able not to exist]; rather, it must be that there is something necessary in the world. Now every necessary being either has a cause of its necessity from outside itself or it does not. But it is impossible to go on to infinity among necessary beings that have a cause of their necessity—in the same way, as was proved above, that it is impossible to go on to infinity among efficient causes. Therefore, one must posit something that is necessary per se, which does not have a cause of its necessity from outside itself but is instead a cause of necessity for the other [necessary] things. But this everyone calls a God.

Fourth way

Summa Theologica  I, Q 2, A 3 Paragraph 4

The fourth way is taken from the gradations that are found in the world:

In the world some things are found to be more and less good, more and less true, more and less noble, etc. But more and less are predicated of diverse things insofar as they approach in diverse ways that which is maximal in a given respect. For instance, the hotter something is, the closer it approaches that which is maximally hot. Therefore, there is something that is maximally true, maximally good, and maximally noble, and, as a result, is a maximal being; for according to the Philosopher in Metaphysics 2, things that are maximally true are maximally beings.

But, as is claimed in the same book, that which is maximal in a given genus is a cause of all the things that belong to that genus; for instance, fire, which is maximally hot, is a cause of all hot things. Therefore, there is something that is a cause for all beings of their esse, their goodness, and each of their perfections—and this we call a God

Fifth way

Summa Theologica  I, Q 2, A 3 Paragraph 5:

The fifth way is taken from the governance of things:

We see that some things lacking cognition, viz., natural bodies, act for the sake of an end. This is apparent from the fact that they always or very frequently act in the same way in order to bring about what is best, and from this it is clear that it is not by chance (non a casu), but as the result of a tendency (ex intentione), that they attain the end.

But things lacking cognition tend toward an end only if they are directed by something that has cognition and intellective understanding (non tendunt in finem nisi directa ab aliquo cognoscente et intelligente), in the way that an arrow is directed by an archer. Therefore, there is something with intellective understanding by which all natural things are ordered toward an end—and this we call a God

There ya go.

Last edited by iwpoe (8/23/2016 3:03 pm)

Yes my intention is to start the ball rolling (if enough people are interested) to begin with each of the five ways, discuss the common misconceptions, the strengths, the weaknesses and the metaphysics in each etc. Have people contribute and in doing so build up some material on each of them that would help other people as well. Thanks for the vote and also for the comments.

Your best bet may be to use Paul Weingartner’s God’s Existence. Can It Be Proven? A Logical Commentary on the Five Ways of Thomas Aquinas. He has the originals, the originals rendered in premise-conclusion form, reconstructions in symbolic logic to prove validity, and extensive commentary on fine points (e.g. Aquinas and Aristotle’s “temporal” modal logic for the Third Way).

9
Not everyone interested votes.