Aquinas' 5th Way
Aquinas argued from a viewpoint of design qua regularity, and was heavily influenced by Aristotle, as he uses' Aristotle's concept of a first cause as God.
In his Summa Theologica, Aquinas presented five different arguments for the existence of God, known as Five Ways. The fifth and final Way of these arguments is an argument from the stance of design:
Things that lack intelligence, such as natural bodies, all act for an end. This is evident because they always, or nearly always act in the same way, in order to achieve the best result.
For example, trees, dogs and mountains all work towards an end. Trees give out oxygen, dogs seek out, eat food and breed, and mountains are complex ecosystems.
All things on the earth work together and separately for their own benefit and for the benefit of the planet as a whole, and follow natural and scientific laws.
Everything achieves its end, and this cannot be down to chance. The laws of science work in such a way that everything functions properly, so the universe must be designed.
Whatever lacks intelligence cannot move towards an end without being directed by something with knowledge and intelligence.
If you're a dog, a tree or a mountain, for example, you cannot deliberately choose to reach your end, as it takes something with intelligence to direct you to do so.
For example, an arrow is shot in a particular direction by an archer. The arrow could not have reached its intended target without the archer's direction.
Aquinas believed that there must be some intelligent being which directs natural things towards their ends through the establishment of natural laws, and this is the being we call God.
Aquina's argument is design qua regularity because it relies on the idea that things follow a set of laws to get their ends.
These laws are scientific, predictable and regular, a good example being the law of gravity.