The argument from design

In the Summa Contra Gentiles St. Thomas sketches the argument like this:

It is impossible that contrary and dissonant things can harmonize in one order always or usually except by someone's governance, by which each and all are made to tend to a certain end.

This argument goes further than the earlier arguments, because the conception of God that it relies on is as the ruler of the universe (“governance” here just means control). And the idea of God as the ruler of the universe comes closer to the conceptions of God that most believers seem to have had.

Now, with any argument, as I pointed out in 3.9, we can distin­guish between the question of whether it is valid—which it is if the conclusion would follow if the premises were true—and the ques­tion of whether it is sound—which it is if the premises are true as well. In considering whether we should believe the conclusion of an argument, we need, then, to keep track both of the truth of the premises and of the validity of the form of the argument.

What exactly is the argument? Well, like all a posteriori argu­ments for God's existence, it will have among its premises at least one (alleged) matter of fact. That fact is that things in the universe harmonize. So let's call this first premise “the harmony of nature.” A second claim, whose status is a little less clear, is that only gover­nance produces harmony. I say that it's a little less clear because, in this outline of the argument, Aquinas doesn't indicate whether he thinks this is something that we know a priori or a posteriori. Let's call this premise “the necessity of a creative intelligence.”

So we have:

1) The harmony of nature

Many things in the universe work together in harmony.

2) The necessity of a creative intelligence

Harmony is always the product of a creative intelligence with a mind.

So: The universe is the product of a creative intelligence with a mind.

This looks like a valid argument. If the premises are true, the con­clusion will be. So what about those premises?