Intelligent Design: Affirming the Consequent

As one who is attempting to educate themselves on anti-evolution demagogy, I often hear recited by proponents of intelligent design theory a variant of the teleological argument. The classic teleological argument read as follows:

1. Every design has a designer
2. The universe is designed
3. Therefore, the universe has a designer

However, when we do a proper logical computation of the above argument, one finds that the argument is not sound under all variants.

Let us use the ID variant. Intelligent design proposes that, based on characteristics of a known designer, we can infer a designer from objects that possess certain attributes of design. That is, we know intuitively what occurs when a designer is present, and therefore it seemingly logically follows that we can infer a designer from the designed. That is: "If designer, then design".

So as to avoid confusion, that me rephrase the sentence as follows: "If designer, then complex specified information". Complex specified information is a term coined by IDists, so I will use that term (which is logically equivalent to the "design" mentioned earlier) so I can use intutive symbols to represent the atomic sentences or arguments as

D -> C

were D is designer and C is complex specified information. Now, the IDist claims that complex specified information exists, and that the existence of said complex specified information provides evidence of a designer. However, we see in the construction above that the designer is the antecedent of the conditional sentence and the complex specified information is the consequent. This does not bode well for the IDist.

In logic, it is a non-trivial fashion to show that affirming the consequent is a logical fallacy that renders an argument unsound. The argument is unsound simply on the basis of the definition of a conditional sentence. A conditional sentence is only considered false in a truth analysis when the consequent is false. The sentence is true so long as the consequent is true independent of the truth or falsity of the antecedent. Therefore, one cannot derive a truth-value from analyzing a conditional sentence "backwards" which is the case of the IDist.