Supporters and researchers of parapsychology insist that it is a valid field of scientific study and that the work being done is fundamentally scientific in nature. Skeptics and those involved in other, more traditional areas of scientific research usually disagree, arguing that it is a pseudoscience at best. Is it possible to resolve this debate?
Criteria of Science
Actually, there is — science is not just some random collection of fields of research. Although the boundaries between science and non-science are not always sharp and clear, there are nevertheless some important principles that are supposed to characterize genuine science. When a research field possesses these characteristics, it's reasonable to call it a science. When not, then it's not a science — and may instead simply be a pseudoscience.
Scientific theories are falsifiable, and one of the characteristics of pseudoscience is that pseudoscientific theories are not falsifiable, either in principle or in fact. The principle of falsifiability or falsification was originally conceived of by Sir Karl Popper, an Austrian-born, British philosopher of science. According to Popper, it is the ability to falsify a theory that makes it scientific, not the ability to verify it.
Proof & Verification
Most people have tended to assume that theories are "proven" and made more "scientific" through the accumulation of evidence that appears to verify it. This is not unreasonable, and it is certainly true that mountains of evidence that verify what a theory says count as good reasons to believe it. That does not, however, make the theory more scientific. After all, one might have constructed a theory that "explains" everything and is readily "verified" because it manages to avoid saying anything too specific.
What falsifiability means is that, in principle, there must be some possible state of affairs which would be incompatible with the truth of the theory. To put it another way, supporters must admit to the possibility that their theory is false, and furthermore have some idea in mind for how that might be demonstrated. Experiments are designed to test for exactly that state of affairs — if it occurs, then the theory is false. If it doesn't, then the possibility that the theory is true is made stronger.
Testing a Theory
Of course, reality is a little more complicated than this. It would be irrational to toss out a theory because of a single instance of alleged falsification, a single experiment that produces results contrary to the truth of the theory. For this reason, no one actually recommends such a course of action. If such results are produced, the proper thing to do is study them and construct more experiments in order to see if they can be reproduced.
Perhaps the results were a fluke. Perhaps they occurred because of some flaw in the original experiment. Perhaps they weren't a fluke but all that is required is a slight adjustment in theory. If any of this is true, then it will come out in the studies and in further experiments.
On the other hand, if further experiments confirm that the original data was accurate, then the principle of falsification kicks in: we have demonstrated the truth of a state of affairs that is incompatible with the truth of the theory. Unless that theory is radially altered, it has to be discarded.
Parapsychology & Falsifiability
In parapsychology, there does not appear to be any state of affairs that would count against the truth of parapsychological claims. Parapsychological researchers are very adept at coming up with all sorts of explanations for how and why their experiments fail — there are too many skeptics near by, the time of the day is wrong, the subject was just having a bad day, etc.
Parapsychologists may continue to latch on to even the weakest sorts of evidence in order to support their claims, but their repeated failures to find evidence are never allowed as evidence against their theories. It is true that there are scientists who have worked this way, but its appearance as a pattern in parapsychology indicates that parapsychology is a pseudoscience rather than a science.
Now, all of their rationalizations might in fact be true — there is nothing in principle that would prevent parapsychological powers from being conveniently sensitive to the presence of skeptics, for example. Yet this does not let parapsychologists off the hook because regardless of how difficult these powers may be to work with and study, the burden rests with them to come up with experiments and predictions which serve to either confirm or falsify their claims.
Given that no one in the field has managed to do this, it is reasonable for observers to conclude that parapsychology is probably not falsifiable and, hence, not science.
