The denier that ID [Intelligent Design] is science faces the following dilemma. Either he admits that the intervention of such a designer is possible, or he does not. If he does not, he must explain why that belief is more scientific than the belief that a designer is possible. If on the other hand he believes that a designer is possible, then he can argue that the evidence is overwhelmingly against the actions of such a designer, but he cannot say that someone who offers evidence on the other side is doing something of a fundamentally different kind. All he can say about that person is that he is scientifically mistaken.
(Thomas Nagel, "Public Education and Intelligent Design," Philosophy & Public Affairs 36 [spring 2008]: 187-205, at 195)