Jerry Coyne asks, “Is falsifiability a good criterion for a scientific theory?” My short answer is “No”, but I’ll try to flesh that out. Coyne writes:
The “theory” of evolution, for example, could be disproven if we regularly found well-dated fossils out of the proper order (like mammals in the Devonian, for instance), if species didn’t have genetic variation to respond to selection, or if we often found “adaptations” in member of one species that were useful only for another species (e.g., a special nipple on a female mole that was only used for suckling mice).
I’ll disagree with that. If the theory of evolution (let’s assume neo-Darwinian theory) were falsifiable, then the discovery of horizontal gene transfer should have already shown it false. If, however, the theory is a framework that functions as a guide to research, then it is neither true nor false. It will be retained as long as it continues to be useful as a framework. Minor discrepancies, such as horizontal gene transfer, can easily be absorbed into that framework.
My view is that a scientific theory exists as such a framework, and is measured pragmatically (by its usefulness), rather than on a true/false basis.
I’m told that falsification is naive as a criterion for good science, and that scientists no longer accept or use that as a criterion.
I’m not convinced that scientists ever used it, except to make rhetorical points (such as in arguments with creationists). I would reword that as “many philosophers no longer say that scientists use falsifiability as a criterion.”
Is there any scientific fact or theory that is widely accepted despite the fact that it is not in principle capable of being falsified?
It’s difficult to say. But take the ideal gas laws of physics. As applied to an ideal gas, they are unfalsifiable, because ideal gases exist only in our minds. As applied to real gases, those laws are well known to be false, but are still useful as a close approximation. If they are known to be false, but still used, does that make them unfalsifiable?
For facts, consider the fact that, during the Newtonian era, the mean solar day was 24 hours long. This was unfalsifiable, because it was the definition of the units of time. It was very much used as a scientific standard. If we look at any scientific standard today, that standard, expressed as a proposition, will be unfalsifiable because it is true by definition. It is my impression that Popper’s criterion was specifically aimed at propositions that are true by definition. But, if applied consistently, it should have ruled out all scientific standards. Fortunately, nobody tried to use it that way.
It is my impression, for instance, that string theory in physics isn’t widely accepted as true simply because we haven’t found a way to test it—to test that its predictions are verified or not.
That’s my understanding. I never did consider it a scientific theory. I looked at it as a speculative hypothesis. The problem, as I understand it, is that they were never able to find a way of connecting the terms of string theory to real empirical data. So it fails the usefulness test. And that requirement, that the terms of a theory should be able to be connected to empirical data, and that the theory prove useful after making that connection — that is what should have been the demarcation criterion.
The Heretical Philosopher 