- In order to clarify the situation, it is important to understand how the underdetermination thesis is established; then, its meaning and its limitation become much clearer. Here are some examples of how underdetermination works; one may claim that:
- The past did not exist: the universe was created five minutes ago will all the documents and all our memories referring to the past in their present state. Alternatively, it could have been created 100 or 1000 years ago.
- The stars do not exist: instead, there are spots on a distant sky that emit exactly the same signals as those we receive.
- All criminals ever put in jail were innocents. For each alleged criminal, explain away all testimony by a deliberate desire to harm the accused, declare that all evidence was planted by the police and all confessions were obtained by force.
Of course, all these "theses" may have to be elaborated, but the basic idea is clear: given any set of facts, just make up a story, no matter how ad hoc, to "account" for them without running into contradictions.
It is important to realize that this is all there is to the general (Quinean) underdetermination thesis. Morever, this thesis, although it played an important role in the refutation of the most extreme versions of logical positivism, is not very different from the observation that radical skepticism or even solipsism cannot be refuted: all our knowledge about the world is based on some sort of inference from the observed to the unobserved, and no such inference can be justified by deductive logic alone. However, it is clear that, in practice, nobody ever takes seriously such "theories" as those mentioned above, any more than they take seriously solipsism or radical skepticism. Let us call them "crazy theories" (of course, it is not easy to say what it means for a theory to be non-crazy). Note that those theories require no work: they can be formulated entirely a priori. On the other hand, the difficult problem, given a set of data, is to find even one non-crazy theory that accounts for them. Consider for example a police enquiry about some crime: it is easy enough to make up a story that "accounts for the facts" in an ad hoc fashion (sometimes lawyers do just that); what is hard is to discover who actually commited the crime and to obtain evidence demonstrating that beyond reasonable doubt. Reflecting on this elementary example clarifies the meaning of the underdetermination thesis. Despite the existence of innumerable "crazy theories" concerning any given crime, it sometimes happens in practice that there is a unique theory (i.e. a unique story about who commited the crime and how) that is plausible and compatible with the known facts; in that case, one will say that the criminal has been discovered (with a high degree of confidence, albeit not with certainty). It may also happen that no plausible theory is found, or that we are unable to decide among several suspects which one is really guilty: in these cases, the underdetermination is real.
One might next ask whether there exist more subtle forms of underdetermination than the one revealed by a Duhem-Quine type of argument. In order to analyze that question, let us consider the example of classical electromagnetism. [...]
- Let's call a philosophical position crazy if it's strongly contrary to common sense and the overall state of scientific and other evidence doesn't decisively support it. So, for example, panpsychism -- the view that all objects have minds -- would appear to be crazy. So would solipsism, the view that I am the only being who exists in the universe. So would radical inductive skepticism, the view that we cannot be justified in believing that the sun will rise tomorrow or that grass will by and large remain green. Of course, if the ultimate weight of evidence decisively supported one of these philosophical positions, that position would no longer be crazy. Heliocentrism and special relativity might have been crazy when first conceived but scientific evidence soon rendered them non-crazy. I assume this is not the case for panpsychism, solipsism, or radical inductive skepticism.
Now, crazyism. Crazyism about a topic is the view that something crazy must be among the core truths about that topic. Crazyism can be justified when we have good reason to believe that one among several crazy views must be true but where the balance of evidence supports none of the candidates strongly over the others. [...]
Perhaps crazyism is justified regarding interpretations of quantum mechanics. [...] I am inclined to think that crazyism is also a justifiable attitude to take toward the relationship between conscious experience and the physical world. All viable options are, when closely examined, strongly contrary to common sense, and none is decisively supported by the overall state of the evidence.