Is the falsifiability rule falsifiable?
Is the proposition "Only falsifiable propositions have scientific value" itself falsifiable?
If you really want to get into the weeds:
Per Descartes, you really can't be 100% certain of anything except the raw fact of your own existence. And even that only works if the Law of Non-Contradiction (or a near-identical analogue) is absolutely true.
That includes any private mystical experiences, which could easily be a delusion, or generated by an Evil Cartesian Demon that seeks to deceive you about the world.
Further, per Hume: We can be 100% certain of deductions, as they are the result of logical operations. We can't be 100% certain of inductions, since it may turn out that at any moment, there can be exceptions to past observations. However, it is still rational to be confident in inductions, as more evidence is accumulated.
I think we can say that everyone has a degree of faith that the world is what they think it is, including die-hard empiricists and philosophical realists (however much they may protest this.) However, there is no way to
exclusively attack empiricism or realism on this basis. If we can't have faith that the real world is real, then why should we believe some alternative claim? Radical rejections of realism are self-defeating.
In terms of falsifiability: The definition of falsifiability, and operations to determine if a type of knowledge, isn't an empirical claim; it's a logical deduction. We define falsifiability, and apply that criteria to different types of claims. We can certainly debate the
merits and limits of distinguishing falsifiable and unfalsifiable claims, and we can use both deductions and inductions to ask whether X is falsifiable or unfalsifiable. But there isn't a need to generate an infinite regress of the very nature of falsifiability.
How does falsifiability apply to this context? At a minimum, something that is falsifiable -- even if not with 100% certainty -- can be said to justify a high degree of confidence. If you believe that the real world exists, that evidence can be discoverable, that attempts to cover tracks are discoverable, then you can reasonably determine the veracity of "Visbek gave ionu Hep C." Claims that Hep C is not always chronic, or that the viral load can drop to 0 on its own, are empirically testable and/or observable. We may also note that at least so far, there is no evidence that spontaneous recovery from illnesses correlates in any way to the beliefs or devoutness of the patient.
In contrast, it's hard to see what standards, if any, can be applied to unfalsifiable claims. One good way to illustrate this is by positing the existence of a demiurge. In this hypothetical, there is some type of creator deity (or not...) that generated the universe, then goes off to play chess for eons, and doesn't care about any sentient creatures in the universe. The demiurge is less powerful than the creator deity, but powerful enough to create the Earth, all its inhabitants, and can manipulate everything on the planet, and treats it like an experiment or a toy -- i.e. it is not benevolent, and doesn't care about humans any more than a scientist cares about paramecium in the lab.
How can you prove that Jesus is real, and the demiurge is not? You can't. Any information you have about Jesus, including private mystical experiences and the production of canonical literature, could have been generated by the demiurge. You might
think that belief in Jesus is more reasonable, but that can also be under the influence of the demiurge when making that claim, either indirectly after years of living in a demiurge-controlled world, or directly by the demiurge making you think that "Jesus is real." The nature of the demiurge blocks you from access to information which could prove or disprove its existence and/or interference.
Thus, we have at least one problem with declaring that "God did not make me sick, but Jesus healed me." There is no real way to make that claim, because
you have no way to know. You don't have sufficient information to make reliable conclusions about the motivations of supernatural beings, because once you license the possibility that these unfalsifiable claims are valid, you cannot contain the consequences of accepting that type of claim. You cannot rule out that the demiurge made ionu sick, and healed him (or didn't) just as capriciously.
So ionu can believe whatever he wants, but... I don't see how or why anyone else should accept it as evidence of anything other than ionu's personal belief system.
