Philosopher Thomas Nagel, writing in the journal Philosophy and Public Affairs, criticizes the exclusion of Intelligent Design from science classes on the grounds that evolutionary science too rests on an assumption: the naturalistic assumption. He argues that both evolution based on natural selection and ID have untestable assumptions.
Frankly, I think that Nagel is wrong partly because he doesn’t understand the people pushing ID and partly because he doesn’t understand science. With respect to the first, he seems to give the IDers like Michael Behe credit as honest brokers pushing a position of principled skepticism rather than backdoor Creationism. So be it. I think that he is being dangerously naive to do that, but I don’t like to start an intellectual argument by impugning the motives of the opposition.
What I will argue is that Nagel is wrong to characterize ID as science because the naturalistic assumption is intrinsic to the definition of science.
Nagel argues that because evolution operates with the a priori assumption of a naturalistic explanation — allowing no supernatural intervention — it is not being scientific:
The claim that ID is not a scientific theory implies that even if there were scientific evidence against evolutionary theory, which was originally introduced as an alternative to design, that would not constitute any scientific evidence for ID. We might have to give up evolutionary theory, but then we would be constrained by the canons or definition of science to look for a different scientific, i.e., nonpurposive, explanation of the development of life, because science prohibits us from even considering ID as a possible alternative explanation, one whose eligibility would otherwise be enhanced by the rejection of the leading scientific explanation, namely evolutionary theory.
What would it take to justify the claim that there are propositions such that the discovery of evidence against them can qualify as science, but evidence in favor of them cannot? Someone who accepts this view would probably extend it to propositions about ghosts or extrasensory perception. Research showing that effects that some benighted souls have attributed to ghosts or mental telepathy can be explained in a perfectly naturalistic way would count as science, but any argument that the evidence does not support those explanations, and that significant experimental or observational data are better explained by ghosts or by ESP, would not count as science, and could therefore be ruled out of consideration. On this view it would not even be a false scientific claim.
The idea is that any naturalistic or nonspiritual explanation of a phenomenon can be either confirmed or disconfirmed by empirical evidence together with causal and probabilistic reasoning. No empirical evidence against such a nonspiritual alternative, however, nor any other kind of empirical evidence, could provide a reason for believing the spiritual hypothesis. Belief in something like that is necessarily the result of a different cognitive process, having nothing to do with the scientific evaluation of empirical evidence (rank superstition or blind faith, to give it its true name). I submit that this way of drawing the boundaries around science depends not on a definition but on the unspoken assumption that all such propositions are obviously false — there are no ghosts, there is no ESP, and there is no god — so that to invoke such things to explain any observed phenomenon, even one for which no other explanation is available, reveals a disposition to take seriously a possibility that a rational person would not consider. Without this assumption the exclusion of ID from consideration cannot be defended.
In order to think that the refutation or very low probability of all the available alternatives provides some evidence for an explanation E of some observation, one has to believe that E is at least possible. So if one thinks that the existence of ghosts is not a possibility, no spooky manifestations, however elaborate and otherwise inexplicable, will be taken as evidence, however weak, that a ghost is behind them. The real issue over the scientific status of ID is over what determines the antecedent belief in the possibility that a nonphysical being should intervene in the natural order. Opponents of the scientific status of ID are moved by the fact that those who believe this is possible, and who therefore can regard certain empirical observations as evidence for its actuality, usually believe in the possibility as a result of faith or ecclesiastical authority, rather than evidence. This nonscientific element, which is a necessary condition of their interpretation of the empirical evidence, is thought to undermine the scientific status of the whole position.
Unfortunately it also seems to undermine the scientific status of the rejection of ID. Those who would not take any amount of evidence against evolutionary theory as evidence for ID, like those who would not take evidence against naturalistic explanations of spooky manifestations as evidence for the presence of a ghost, seem to be assuming that ID is not a possibility. What is the status of that assumption? Is it scientifically grounded? It may not be a matter of faith or ecclesiastical authority, but it does seem to be a basic, ungrounded assumption about how the world works, essentially a kind of naturalism. If it operates as an empirically ungrounded boundary on the range of possibilities that can be considered in seeking explanations of what we can observe, why does that not undermine the scientific status of the theories that depend on it, just as much as a somewhat different assumption about the antecedent possibilities? (Emphasis mine.)
Nagel is arguing as if the presence of the assumption of naturalism is inherently anti-scientific. He presents science as a method for dealing with evidence without any biases about the nature of that evidence.
The problem with this point of view is that it is a caricature of the scientific method. Yes, science includes a method of dealing with evidence, but it also includes the naturalistic assumption about that evidence. Science divides evidence into what is admissible and what is not. There is a reason that before the term “scientist” was coined the term commonly used was “natural philosopher.” This is because science deals with the class of phenomena that physically exist in nature. It has nothing to say about supernatural phenomena; it’s principles do not apply there.
I think that Nagel is confusing science with philosophy. Philosophy — and more importantly logic — is a method of evaluating evidence that does not privilege one type over another. Science, on the other hand, does privilege evidence. We only deal with natural evidence. Thus, the statement that science should admit ID to avoid making an unscientific assumption is a non sequitur. It is like arguing that algebra should admit other maths that violate the transitive property because algebra assumes the transitive property. I agree that there are other maths. I agree that those maths may have meaning or usefulness. I just reject the notion that the place for them is in algebra.
Nagel also seems to be frustrated with the normative nature of the naturalistic assumption. This is just silly. The selection of particular books to be read in English class is a normative assumption. It is based on what the teachers feel is most useful. More importantly, you would never ask an English teacher to include books in French because the “decision to include only books in English is a normative one.” There is a place for French books: French class.
Further, if you want to argue for the usefulness of assumptions, you would be hard pressed to find one more useful than the naturalistic assumption. Let’s set aside the fact that all the wonders of the modern world are predicated on an assumption of physicality. (No one thinks prayer will move the subway.) Let’s make a wager. Give me one person who believes in spirit healing and one person who believes in science, and let’s see who cures AIDS first. My money is on the scientist. Naturalism is the most experimentally verified assumption in the history of humanity.
I am perfectly willing to admit to Nagel (or anyone else) that science has assumptions about the world. I am intellectually honest enough to admit that naturalism is an assumption — albeit a well-tested one. What I suggest is that this assumption is so intrinsic to science that to abandon it would corrupt and destroy the entire enterprise. Nagel seems to believe that if we just let the IDers in but qualify their entrance with the statement that, “there really is little evidence for their beliefs,” everyone will be satisfied and life can go on. I counter that to do that we would have to sacrifice science on an altar of superstition. You cannot run an experiment assuming that there is a non-zero probability that an angel changed the results. If there is a non-zero probability that angels are interested in experimental findings, then all the experiments I have ever done are rendered uninterpretable.
Let me get some things straight, though. I don’t think it is wise for scientists to push the argument of how science negates religion. I think that is a bad political choice for reasons that I have discussed before. Further, in great contrast to many of my liberal friends, I don’t give a rat’s ass what the IDers choose to teach their children. They are more than welcome to teach whatever perverse twaddle they choose to dignify with the term “science.” In doing so they will likely render their children incompetent for anything other than an evangelical world, but so be it. I will even go so far as to say that I do not like the idea of “public” education because it puts me in the position of needing an opinion about how other people raise their children. I would much prefer a system of school choice.
However, this is the situation we are in, and we had better make the best of it. So long as we have “public” education, scientists and educators will continue to argue that ID is by definition non-science and therefore has not place in science class. Science by definition includes the naturalistic assumption. You could — if it were legal — teach ID in any other course you like, but not in science class. This is the essence of Stephen Jay Gould’s idea of Nonoverlapping Magisteria — a notion with which I wholeheartedly agree:
The lack of conflict between science and religion arises from a lack of overlap between their respective domains of professional expertise — science in the empirical constitution of the universe, and religion in the search for proper ethical values and the spiritual meaning of our lives.
ID, because it requires supernatural causes, simply does not fall into the realm of science.