Paley:
"In crossing a heath, suppose I pitched my foot against a stone, and were asked how the stone came to be there; I might possibly answer, that, for anything I knew to the contrary, it had lain there forever: nor would it perhaps be very easy to show the absurdity of this answer. But suppose I had found a watch upon the ground, and it should be inquired how the watch happened to be in that place; I should hardly think of the answer I had before given, that for anything I knew, the watch might have always been there...every indication of contrivance, every manifestation of design, which existed in the watch, exists in the works of nature; with the difference, on the side of nature, of being greater or more, and that in a degree which exceeds all computation."
Problems:
1. A contradiction. First Paley distinguishes the watch from nature, but then attempts to create an analogy simply through complexity. Complexity does not denote design.
2. The materials to make the watch already exist, but then we have to believe that a creator made the universe out of nothing.
3. False analogy:
A watch is complex
A watch has a watchmaker
The universe is also complex
Therefore the universe has a watchmaker
Then it should apply elsewhere:
Leaves are complex cellulose structures
Leaves grow on trees
Money bills are also complex cellulose structures
Therefore money grows on trees
Like most analogies, it is somewhat weak and it ignores important aspects: it does not tell us who is the watchmaker, it merely assumes it is a god, therefore it is not sound evidence for a god, and like the cosmological argument it breaks down at the point where one enquires, who made the watchmaker?
Although I try to avoid using Dawkins as a source owing to an irrational hatred of the man evinced by those who cannot disprove his claims, he sums it up perfectly:
"Paley's argument is made with passionate sincerity and is informed by the best biological scholarship of the day, but it is wrong, gloriously and utterly wrong. The analogy between telescope and eye, between watch and living organism, is false. All appearances to the contrary, the only watchmaker in nature is the blind force of physics, albeit deplored in a special way. A true watchmaker has foresight: he designs his cogs and springs, and plans their interconnections, with a future purpose in his mind's eye. Natural selection, the blind unconscious, automatic process which Darwin discovered, and which we now know is the explanation for the existence and apparently purposeful form of all life, has no purpose in mind. It has no mind and no mind's eye. It does not plan for the future. It has no vision, no foresight, no sight at all. If it can be said to play the role of watchmaker in nature, it is the blind watchmaker."
The Blind Watchmaker Richard Dawkins, 1986