Both the Cosmological and Teleological (Design) argument for the existence of God argue "a posteriori", in that, they look to science to substantiate God's existence. Whereas the crucial notion of the cosmological argument is causality, the teleological argument (from the Greek word "teleos" meaning "end" or purpose) argues qua regularity and qua purpose(1). Design arguments are arguments from analogy(2); the universe is analogical to things within it and therefore like these, must have a cause. .
The most famous example of analogy qua purpose was by William Paley(3) "Just as a watch is a complex mechanism, having parts which co-operate so as to achieve a certain end, namely the measurement of time, so for example the eye is a highly complex system having parts which co-operate to provide information about its environment to the organism". The watch was designed by an intelligence with a purpose in mind, similarly that living things are as they are, is a testimony to the existence of a creator.
St Thomas Aquinas held that things which lack knowledge, such as an acorn cannot strive towards a goal (i.e. grow into an oak tree) unless it is directed by an intelligent being(4).
The arguments from design qua regularity are best exemplified by F.R Tennant in his Anthropic Principle(5) and Richard Swinbourne in his probabilistic teleological argument. Both hold that the complexities of the universe are too specific, for example the charge on an electron, to have occurred by chance. "It is extremely improbable that the laws of the universe should be so balanced as to permit development of life unless we adopt the hypothesis that these laws were fixed by a creator who desired the development of life"(6).
The argument from design faces the same kind of objections as the cosmological argument, it takes a certain concept out of the context in which it applies. With the cosmological argument this concept was causation, in the teleological argument it is design.