This week, a federal judge ruled that intelligent design may not be taught in the science classrooms of Pennsylvania's public schools. I agree with the verdict, but we need to be careful about our reasons for supporting it. Most critics of intelligent design seek to undermine it by arguing that the doctrine is not science. It's actually religion passing itself off as science. Hence, its teaching constitutes religious instruction. The Constitution disallows the state's establishment of religion. Therefore, intelligent design cannot be taught in the classroom.
The problem with this argument is that it requires making the case that intelligent design is not science. And the intelligibility of that task depends on the possibility of drawing a line between science and non-science. The prospects for this are dim. Twentieth-century philosophy of science is littered with the smoldering remains of attempts to do just that.
Science employs the scientific method. No, there's no such method: Doing science is not like baking a cake. Science can be proved on the basis of observable data. No, general theories about the natural world can't be proved at all. Our theories make claims that go beyond the finite amount of data that we've collected. There's no way such extrapolations from the evidence can be proved to be correct. Science can be disproved, or falsified, on the basis of observable data. No, for it's always possible to protect a theory from an apparently confuting observation. Theories are never tested in isolation but only in conjunction with many other extra-theoretical assumptions (about the equipment being used, about ambient conditions, about experimenter error, etc.). It's always possible to lay the blame for the confutation at the door of one of these assumptions, thereby leaving one's theory in the clear. And so forth.
Let's abandon this struggle to demarcate and instead let's liberally apply the label "science" to any collection of assertions about the workings of the natural world. Fine, intelligent design is a science then - as is astrology, as is parapsychology. But what has a claim to being taught in the science classroom isn't all science, but rather the best science, the claims about reality that we have strongest reason to believe are true. Intelligent design shouldn't be taught in the science classroom any more than Ptolemaic astronomy and for exactly the same reason: They are both poor accounts of the phenomena they seek to explain and both much improved upon by other available theories.
The suspicion that religion is lurking somewhere in intelligent design theory is correct, but its locus is often misidentified. The religion isn't in the claims of intelligent design themselves. Rather, the religion is in the motivation for pushing a poor account of the natural world into the science curriculum.
I think there are two reasons why people shy away from this way of viewing the matter. First, if you call intelligent design "poor science," then it seems you've allowed intelligent design a foot in the door by accepting that it's science. Science versus non-science seems like a much sharper dichotomy than better versus worse science. The first holds out the prospect of an "objective" test, while the second calls for "subjective" judgment. But there is no such test, and our reliance on judgment is inescapable. We should be less proprietorial about the unhelpful moniker "science" but insist that only the best science be taught in our schools.
The second reason has to do with politics. The courts have had something to say about the constitutional guarantees of the separation of church and state. They've had nothing to say about the unconstitutionality of teaching bad science. Hence, if you wish to use the courts to stop school boards from introducing intelligent design into the curriculum, it seems you've got to argue that intelligent design isn't a science but a religious doctrine. If we're to be honest, either we should find alternatives to the courts to protect our curricula from bad science, or we should start arguing in court that the separation of church and state would be violated by intelligent design's injection into the science curriculum on account of its predominantly religious motivation.
• Alexander George is a professor of philosophy at Amherst College.