 Popper thus calls enumerative induction, then, "a kind of optical illusion"—shrouding steps of conjecture and refutation during a "problem shift".Still, debate continued over the problem of induction, or whether it poses science a problem.Some have argued that although inductive inference is often obscured by language—as in news reporting that experiments have proved a substance is to be safe—and that enumerative induction ought to be tempered by proper clarification, inductive inference is used liberally in science, that science requires it, and that Popper is obviously wrong.