The central tenet of Intelligent Design is usually stated as “certain features of living organisms are too complex to be the result of natural processes, therefore they were designed.”
But as Michael Behe explained at length on the stand in the Dover Panda Trial, what he objects to (at least, when he’s on the stand) is the notion that these features could have been formed by natural selection. He also made it clear that as far as he’s concerned, the designer is God.
So really, the central tenet of ID should be restated as, “certain features of living organisms are too complex to be the result of natural selection, therefore they are the result of a powerful, intelligent, probably supernatural, entity.”
The structure of this argument is exactly the same as, “the Egyptian pyramids could not have been formed by erosion, therefore they were built by space aliens” or “my shirt is not white, therefore it is red.”
Note the change from “natural processes” to “selection”. What ID creationists really want is an argument that proves God. But there’s no evidence for any gods, so they need to use “X cannot be explained by natural means, therefore it involves a supernatural agent.” But you can’t prove a negative. Even a statement like “a perpetual-motion machine is impossible” is really an abbreviation of “if a perpetual-motion machine is possible, then just about everything we know about physics is wrong.”
So they fudge a bit, and extrapolate from “X cannot be explained by natural selection” to “X cannot be explained by natural causes.” But when you restate it that way, it becomes much clearer that “it’s not natural selection, therefore it’s a powerful intelligent being” is a non sequitur.