Advocates of Intelligent Design tend to claim that they aren’t trying to sneak God into the science curriculum. People such as this aren’t helping their cause:
Sharon Lemburg, a social studies teacher, soccer coach and minister's wife, was the ID teacher. She defended the class to a local publication writing, "I believe this is the class that the Lord wanted me to teach."
There are many articles, books, and most recently a court case that explain why intelligent design isn’t science. However, the reason why it is not science need not be so prolix. ID isn’t science because scientific theories don't rely on the Burden of Proof Fallacy.
ID claims that if, in the living world, there are irreducibly complex objects, then evolution by natural (and sexual) selection cannot explain them. If this is the case, they argue, given these structures are complex and clearly have a purpose, they must have been designed by an intelligence. The point to note is that they do not propose how these structures were designed, so in effect their explanation is not an explanation. It explains precisely nothing.
The ID claim boils down to - if you can’t explain this phenomena, then my theory is right. This is certainly not how one argues for a scientific hypothesis, and moreover, it is a fallacious argument. For a theory to be considered plausible there needs to be evidence for it. It doesn't simply "win"* if another theory is missing the occasional explanation (though all the things ID proponents claim evolution can't explain have been explained by evolutionary biologists in an orthodox fashion).
In his book, Just a Theory, Moti Ben Ari proposes what I consider to be a very accurate definition of a scientific theory:
A scientific theory is a concise and coherent set of concepts, claims and laws (frequently expressed mathematically) that can be used to precisely and accurately explain and predict natural phenomena.
A theory should include a mechanism that explains how its concepts, claims, and laws arise from lower-level theories.
ID fails to meet this criteria just a miserably as astrology (say).
Already we've seen some of the major problems with ID. However, it doesn't end yet. The more general argument from design is a False Analogy that Begs the Question. ID proponents argue that we have A - irreducibly complex machines which show structure and order. And we have B - irreducibly complex biological machines, which also show structure and order. We know that A has been created by an intelligent designer (namely us), therefore it follows that B must have also been created by an intelligent designer (namely God). This is a classic, but in the end specious, inductive argument:
All the things in the world we know of, that have been intelligently designed, have certain properties which conclusively demonstrate they have been intelligently designed. It follows then, that anything which also has these properties must also have been intelligently designed.
But all we really know for certain is that human artefacts were made by humans. We don't know for sure that these other 'designed' things are the product of intelligence. In fact this whole argument is circular, it 'begs the question'. It assumes as its premise the conclusion it's trying to demonstrate. It's basically saying, "something that is designed has properties which show it was designed." This conclusion, though tautological, is acceptable. But the next part of the argument is a non-sequitur. "Therefore something which shows these properties was intelligently designed." All we know for sure, is that when humans design something, it inevitably has properties such as complexity, structure, purpose and order etc., but we can't conclusively demonstrate that this reasoning applies in reverse, that complexity, structure, purpose and order, can only be the product of intelligent design.^ They assume a priori, that things which have properties such as complexity and purpose, are a proof of intelligence.
Note that this watchmaker argument from analogy is hardly new.
* If any other theory besides evolution was to "win", I'd be casting my vote for the flying spaghetti monster.
^ BTW - there's nothing wrong, philosophically, to believe the entire universe is designed by an intelligence (namely God) - a masterful programmer who has written intricate laws which govern our existence. But this is a hypothesis which is unable to be tested, one that does not offer any mechanism or precise predictions etc. Ie, it is not science. It is a metaphysical belief. Science and theology are both branches of metaphysics but to try and prove God's existence through science is an ontological error. (On top of which is the problem that it's not possible to prove anything, in the strict sense of the word, except mathematical/logical truisms based on the acceptance of a priori axioms/premises.)
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