Apparently Aquinas’s Fourth Way is considered a strange one, so I thought I’d try describing it, see if I get it right and what others have to say about it.

Aquinas posits being as a transcendental: something that is above every genus and unrestrictedly common to all beings, who all have being in some sense.

Two other transcendentals are truth and goodness: These are convertible with being, which is to say they refer to the same property of being.

“True” here refers to how real or genuine something is. Everything that has being is a somewhat true or real or genuine instance of itself, such as a triangle drawn well or sloppily; the former being more true than the latter. In the same way we can use the word “good” to refer to the former but not so much to the latter. To say that something is true or good here is to say it possesses the property (to some degree) of being what it is.

Proceeding from all this is Aquinas’s Fourth Way:

We can only judge a triangle, say, as being a good triangle by reference to a maximum in being/goodness/truth. No matter how well you draw a triangle, it will always be possible for it to be better, and we know this only because we recognise it does not possess perfect goodness/truth/being. However, it does possess each to a certain degree. To be a degree of something is to participate in a progression which points to a maximum. Something which has maximum being/truth/goodness is simply being itself; something that derives its being not from somewhere else (which would limit it) but from itself, and is therefore the thing from which everything else derives their being/truth/goodness (by their participation in the scale towards the perfection of those things). This is given the name God.