Explain the teleological argument and Hume's criticisms of it.

The teleological argument concerns itself with the ideas of purpose and regularity to argue for the existence of God. The argument is a posteriori, as it derives its evidence from observation of the natural world, and inductive because the truth of the premises does not logically guarantee the truth of the conclusion. One notable proponent of this idea was Thomas Aquinas, who argued for a form of design qua purpose. In Summa Theologica, Aquinas suggested that all objects, including those that lack awareness, demonstrate behaviour towards a certain goal or purpose, and states that there must be some intelligent being guiding these objects. To illustrate this, he uses the analogy of the archer and the arrow. If one were to think of a flying arrow, it clearly lacks awareness but is able to reach its target because it was propelled and guided by an archer. Similarly, any natural unaware object which seems to fulfil a purpose, such as a seed becoming a grown plant, must be guided by God. William Paley also provided an argument from design qua purpose, using the watchmaker analogy. If one were to stumble upon a heath and encounter an old-fashioned watch, which evidently needs a number of complex and intricate parts in order to work towards its purpose of telling the time, it would seem absurd to suggest it had not been created by a skilled watchmaker. Similarly, he believed that if one were to look at, for instance, the human eye, one would reach the same conclusion, that there must have been an intelligent being which designed it for the purpose of sight. Additionally, Paley also argued for design qua regularity, claiming that the precise and regular relationship of planets in orbit could not have arisen by chance. Overall, then, the teleological argument concludes that the purpose and regularity seen in nature must have guided by an intelligent being, and that the intelligent being is God. 
In Dialogues Concerning Natural Religion, however, David Hume raised a number of criticisms against the argument. As an empiricist, Hume claimed that we derive our knowledge of causes from our experiences, and so we can say how a watch is made because people have observed watches being made by craftsmen. No human being, though, was able to witness the beginning of the universe, and so we unable to claim that the analogies between the universe and man-made objects hold. This criticism, then, deals with the causal claim of the argument from observations of purpose and regularity to the conclusion of a designer. Hume also stated that universe is not a machine, like a watch is, and instead holds more in common with organic objects, for which it is less obvious that they have a purpose. Furthermore, even if one were to accept the premises of the argument, one does not have to accept the conclusion that the Judeo-Christian God is the designer. For example, Hume claimed that we can observe a great deal of needless suffering in nature, and this does not point to the designer being a benevolent or perfect being as God is considered to be. If a human invention were to cause excessive suffering, we would deem it a flawed design, and such reasoning could be applied to the universe. Secondly, much like the construction of a house requires a team builders, the premises of the argument do not prevent us from concluding that perhaps a team of gods, for instance, designed the universe. Consequently, Hume not only undermines the premises themselves, but also illustrates that acceptance of the premises gives us no reason to accept the conclusion, and so successfully delivers powerful criticism of the teleological argument.