To prove that a "theory is a true theory" we cannot use the "falsifiability principle".
Popper's does not seem to answer Hume's question. The theory that the sun rises every day may have survived falsification yesterday, but is this a reason for believing that it will survive falsification tomorrow? That was what Hume wanted to know.
Popper retorts that induction is not justifiable. That a theory has been corroborated in the past "says nothing whatever about future performance." Popper wants to say that it is possible to avoid assuming that the future will, or probably will, be like the past, and this is why he has claimed to have solved the problem of induction. We do not have to make the assumption, he tells us, if we proceed by formulating conjectures and attempting to falsify them.
He says that, as a basis for action, we should prefer "the best-tested theory." This can only mean the theory that has survived refutation in the past; but why, since Popper says that past corroboration has nothing to do with future performance, is it rational to prefer this? Fundamental is the question how, even in theory, we can possibly prefer one hypothesis to another, or take one as a nearer approximation to truth than the other, if past corroboration has no implications for the future. Without the inductive assumption, the fact that a theory was refuted yesterday is quite irrelevant to its truth-status today. So demising the inductive assumption makes nonsense of Popper's own theory of the growth of scientific knowledge.
Theories or hypotheses can only be subjected to empirical testing in groups or collections, never in isolation. The idea here is that a single scientific hypothesis does not by itself carry any implications about what we should expect to observe in nature; rather, we can derive empirical consequences from an hypothesis only when it is conjoined with many other beliefs and hypotheses, including background assumptions about the world, beliefs about how measuring instruments operate, further hypotheses about the interactions between objects in the original hypothesis' field of study and the surrounding environment, etc. For this reason when an empirical prediction turns out to be falsified, we do not know whether the fault lies with the hypothesis we originally sought to test or with one of the many other beliefs and hypotheses that were also needed and used to generate the failed prediction. It forms a criticism of methodological falsificationism.
Holist underdetermination ensures there cannot be any such thing as a “crucial experiment”: a single experiment whose outcome is predicted differently by two competing theories and which therefore serves to definitively confirm one and refute the other. Our response to the experimental or observational falsification of a theory is always underdetermined in this way. When the world does not live up to our theory-grounded expectations, we must give up something, but because no hypothesis is ever tested in isolation, no experiment ever tells us precisely which belief it is that we must revise or give up as mistaken. All of the beliefs we hold at any given time are linked in an interconnected web, which encounters our sensory experience only at its periphery.
references: Peter Singer, Quine, Pierre Duhem