Let's start out with the Teleological Argument.
Teleology: the philosophical study of design and purpose. The supposition that there is purpose or direction in the works and processes of nature.
Teleological Argument: the Argument from Design: argues for the existence of god or a creator based on perceived evidence of order, purpose, design or direction in nature.
Here's the basic argument:
- The universe is too complex, orderly, adaptive, apparently purposeful or beautiful to have occurred randomly or accidentally.
- Therefore the universe must have been created by a sentient, intelligent, wise or purposeful being.
- god is a sentient, intelligent, wise or purposeful being.
- Therefore god exists.
You can substitute just about anything in for the universe. The eye, humans, the fundamental constants of the universe, etc.
Many great men have used this argument over the centuries, but that doesn't make it valid. Socrates, Plato, Aristotle and Cicero to name a few. Cicero started the Watchmaker Analogy:
"When you see a sundial or a water-clock, you see that it tells the time by design and not by chance. How then can you imagine that the universe as a whole is devoid of purpose and intelligence, when it embraces everything, including these artifacts themselves and their artificers?" (Cicero, De Natura Deorum, ii. 34)
Even Charles Darwin found the Watchmaker Analogy compelling, which he got from William Paley who wrote about it in his book titled Natural Theology in 1802. But his theory of evolution was an alternative explanation for the complexity of nature. In his autobiography, Darwin wrote,
Although I did not think much about the existence of a personal God until a considerably later period of my life, I will here give the vague conclusions to which I have been driven. The old argument of design in nature, as given by Paley, which formerly seemed to me so conclusive, fails, now that the law of natural selection has been discovered. We can no longer argue that, for instance, the beautiful hinge of a bivalve shell must have been made by an intelligent being, like the hinge of a door by man. There seems to be no more design in the variability of organic beings and in the action of natural selection, than in the course which the wind blows. Everything in nature is the result of fixed laws. (Charles Darwin's Autobiography, page 87)
And of course, proponents of intelligent design find this idea compelling. They make up complicated sounding concepts like irreducible complexity (variation of the watchmaker analogy where you can't have half an eye, you need it fully developed for it to be effective, etc) and other such nonsense.
Just Because It's Complex Does Not Imply A Designer
There are systems in nature that are non-random or orderly simply because they follow natural physical processes. Diamonds and snowflakes are examples.
Just because it's not understood (argument from ignorance) doesn't mean god did it. In many cases its simply the ignorance of the person arguing that god did it. For instance, the eye is seen in many different stages of evolution throughout the animal kingdom today and throughout natural history. All are relevant, all show irreducible complexity to be completely nonsensical.
Listen to Richard Dawkins or Neil deGrasse Tyson and you'll start to see the unsoundness of such arguments. In fact, Dr. Tyson did a 6 minute video about "bad design" which you can find here: By god He's a Bad Designer. This is an interesting angle. If everything was designed by god, why are there so many screwy ways that nature does things? Why are there so many bad designs, like eating and breathing out of the same hole?
Evolution, as Darwin laid out and science has refined, is a better explanation with more supporting evidence than intelligent design could ever hope to be.
Does Not Prove The Existence Of God
Even if, by some twisted perversity everything is designed by a god, it doesn't mean that it is the one god that the christians, jews or muslims follow. It doesn't mean, by that logic that there is just one god at all, or that the designer(s) are omnipotent, benevolent, or even interested in earth.
Voltaire and David Hume came up with those ideas.
If Everything is Designed, Who Designed the Designer?
Or as Richard Dawkins suggests, the teleological argument would apply to the designer in question. So that designer would have to be at least as complex and purposeful as the designed objects. You would need many designers, all even more complex than the previous, to design the designers.
Some say that god is outside of the natural laws of the universe, so that he doesn't need a designer. But this is nonsensical. If he was outside of nature, he would be unable to interact with nature. If you moved the goalposts again to say that he could magically mess with nature even though he is outside of the laws of nature, wouldn't there be some trace of nature being messed with each time? (Just a thought.)
I'm no philosopher. I'm just trying to simply explain this theological argument that we all come across in our travels. Feel free to add to my explanations, give examples, and show counter arguments to help us all understand some of these philosophical concepts.