The design argument is also known as the teleological argument. Telos means goal, aim or purpose. The argument looks at the idea of purpose and order within the universe to argue for the existence of God. The argument is an a posteriori, inductive, synthetic argument. A posteriori arguments have statements that rely on proof from the external evidence. In inductive arguments the argument is only brought in at the conclusion.

Aquinas's 5th way in the cosmological argument as it argues for the existence of God, with regards to the evidence of purpose in nature. Aquinas stated that everything works together in a particular order despite the fact that inanimate objects have no mind or rational powers to achieve this. He explained his point by using the example of an arrow, saying that for an arrow to reach its destination it must be directed first of all by the archer. In the same way ‘natural bodies’ seem to act in a regular fashion to reach a specific purpose. As they, like the arrow, are not able to direct themselves, there must be a first cause. This first cause is what Aquinas considered to be God.
Another philosopher that postulated a teleological argument is Paley. Paley put forward his argument for the existence of God during the period of enlightenment (where science was being used to prove evolution). Paley explained his theory using an analogy of the watch, but drawing comparisons between features of the watch and of the universe. He stated that if a man was walking across a heath and he came across a stone he could assume that the stone came about through nature. However, if he were to come across a watch the same could not be suggested. The watch shows order (cogs, etc) and purpose (telling the time) and therefore it's not reasonable to assume that the watch came about without the agency of a watchmaker. Paley's analogy compared the watch with the universe, arguing that it is equally unreasonable to suggest that universe, with all its details, came about without the agency of a world-maker. Paley proposed that this world-maker is God. The basis of Paley's argument is that there is evidence of design in the universe around us. Everything appears to have been designed to fulfil some function. This argument is Design qua purpose. Paley argued that the way that each aspect of the natural world appears to fulfil its purpose is further evidence of design. Paley therefore argues for a Designing creator - God. Paley goes on to argue that there is further evidence for a creator God in the regularity of the universe. In particular, Paley considered the motion of the planets in the solar system. He argued that the relationships between them and the effect of gravity on them could not have come about without a designing principle at work. The way the universe functions is far too complicated to be a coincidence. This principle is God. This argument is design qua regularity.

On the other hand however philosophers such as David Hume criticised the argument. He set out 2 versions of the design argument. The first of which, relied on an analogy. To which he argued implied a superhuman, anthropomorphic concept of God, which is very limited and inconsistent. The world is imperfect and flawed, and as such it could suggest an imperfect and flawed creator.
Hume's second argument outlined the possibility that the world did come about through chance. He questioned the idea of there just being one God. Why could there not be more than one creator/God? Hume went on to support the idea of natural selection- he claimed that it is entirely plausible that the adaptations made by animals to survive might be the result of random adaptations, rather than the agency of an intelligent designer. Hume also argued that we can only attribute to a cause whatever qualities are needed to produce the effect. So the design argument, if it works only proves the existence of a design producing being. We cannot also say that this being has any of the characteristics traditionally recognised to God. Furthermore, Hume argued that we cannot conclude from the fact that example of order in the universe have human causes that order in the universe as a whole has a cause, because the universe is unique. Therefore the analogy doesn't work because we have no way of knowing whether order and its explanations within the universe are in any way like order and its explanations in the universe as a whole. Hume criticised the analogy in that it was an inaccurate comparison. He argued that are more accurate analogy would be to compare the world with a carrot, and the mark of design perceived in the world could be due to 'generation', 'self-regulation' and 'growth' rather than design. Darwin supported this criticism.

Darwin proposed a theory of the survival of the fittest. He called this principle natural selection. The fittest members of the species survive and their characteristics become part of the character of the species. He therefore argued that the apparent design is in fact the result of a natural and random process. Dawkins supports Darwinian evolution and rejects God.

Mill, another critic of the argument, argues that nature is 'guilty' of serious crimes for which she goes unpunished. The various 'atrocities' through which both humans & animals have suffered would not go unpunished if they were the result of Human agency. Mill therefore concluded that the world cannot be ordered, and he rejects the idea that it is the result of intelligent design. Kant also went against the design argument and noted that the design argument is based on the premise that there is design in the universe. He argued that the universe might be in a state of chaos and confusion. And that our minds assimilate and organise sense experiences into a perceived order. He is basically saying that we do not understand the full extent of the universe yet therefore it may be that it is just a mix of different random things in a chaotic way we don’t as humans fully understand so we cannot judge.

In conclusion Aquinas’s and Paleys proposal of the design argument to justify god existence is a limited metaphorical answer which attempts to outline that, the complexity of the universe contains purpose and order. As a result there must be a designer behind this great design which is god. However their theories and analogies have been weak and are simply not detailed enough to justify the existence of god. This is because other philosophers such as Hume have suggested that these arguments are inadequate, they have also provided more plausible explanations for the complexity of the universe such as the Epicurean Hypothesis. This is an alternative theory talking about the initial universe being chaotic but after a huge amount of time the forces calmed down and naturally ordered themselves. Therefore Philosophers arguing for design in the universe fail to prove gods existence in a convincing manner.