 A natural deductive reasoning form, logically valid without postulates, is true by simply the principle of nonselfcontradiction.A natural deductive form is "denying the consequent"—"If A, then B; not B; thus not A"—whereby one can logically disconfirm the hypothesis A.At least logically, any phenomenon can host multiple, conflicting explanations—the problem of underdetermination—why the move from data to theory lacks any formal logic, that is, any deductive rules of inference.