A couple of posters on LGF (who no doubt are more familiar with Aquinas than I am) have suggested that I misrepresented Aquinas in the argument from design sketched out in the last post. For the record, that sketch is a way of paraphrasing the following quotation, which is from Summa Theologica – First Part – Question 2 – Article 3:
“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.”
Again, my paraphrase:
1) Natural things (even inanimate objects) nearly always act regularly, in such a way as to produce the best results.
2) So, natural things act purposefully, to achieve some goal.
3) If something acts purposefully, it either has a mind, or is designed by something that does.
4) Natural things (such as inanimate objects) do not have minds.
Conclusion: So such natural things must be designed by something that does have a mind (God)
It seems to me that my sketch properly captures the logic of this particular passage, although I am more than willing to be educated otherwise by Aquinas scholars.
By the way, I have great respect for Aquinas. His systematic thought helped to pave the way for modern and contemporary philosophy. And I certainly do not mean to imply that this passage was his final word on reasons to believe in God.