The teleological argument is the design argument for the existence of God. This argument is an a posteriori argument. It is based on observations of the apparent order in the universe and the natural world, to conclude that it is not the result of mere chance but of design. The evidence from design points to a designer and the argument concludes that the designer is God. "With such signs of forethought in the design of living creatures, can you doubt they are the work of choice or design?" Socrates. The design argument is split into two parts: design qua regularity and design qua purpose. For example, the seasons is design qua regularity because it is a repeating cycle of events and if it messed with (weather has sudden change) it will cause everything to go wrong and out of place. An example of design qua purpose is a television it has been designed to produce sound and an image. If all the parts was put in a different order then it would not work, its been manufactured for a certain teleos.
St Thomas Aquinas used a form of the teleological argument in his five ways, this being in his fifth way. He identified that the way in which natural bodies act in regular fashion to accomplish their end provides the evidence for the existence of an intelligent being. People are there to achieve their end not fortuitously but designed. Therefore some intelligent being exists by whom all natural things are directed to their end and this being is called God. Aquinas was arguing from design qua regularity.
In Dialogues Concerning Natural Religion, David Hume criticises the teleological argument; he argued that the Universe was designed does not necessarily mean that God designed it. There is no evidence that the Universe needs a designer it may come into existence naturally. We have no evidence that the Universe was just pure chance.