Full Idea
Things which lack knowledge, such as natural bodies, act for an end, which is usually in the same way, to obtain the best result. Hence they achieve their end designedly. Hence some intelligent being exists by whom all natural things are directed.
Gist of Idea
Way 5: mindless things act towards an obvious end, so there is an intelligent director
Source
Thomas Aquinas (Summa Theologicae [1265], Ia,Q02,Art3,Reply)
Book Reference
'The Existence of God', ed/tr. Hick,John [Macmillan 1964], p.85
A Reaction
[compressed] This is Greek teleology with a vengeance. Plants probably illustrate best what he has in mind. There is obvious teleology in human affairs, and there is a sort of teleology in living things, but we take the end to be reinforced by success.