Scientific hypotheses possess a high status: they are valid. (The word "valid" comes from the Latin for strong.) How do scientific hypotheses acquire validity? This is the problem of validation of scientific hypotheses. It is standard fare: it is the major item of discussion in many philosophical texts especially those devoted to the philosophy of science, be it a textbook or a history or a monograph, in which a valiant philosopher tries afresh to tackle it. Some of the most powerful minds ever have tried to tackle it, yet to no avail. This is hardly surprising, as there is a famous proof that it is insoluble. It is simple: every validation is the application of a criterion that also needs validation. Diverse variants of the proof appeared repeatedly ever since Antiquity. The modern tradition presents it in the variant that David Hume has offered, and as Hume's criticism of induction. Most philosophers today still declare it the most central problem in the philosophy of science, perhaps in philosophy generally: how can we answer Hume's criticism?