 The function of these provisos means that instrumentalist constructions of scientific theories as mere calculating devices and programs for the elimination of theoretical language by reduction to observational language alone are misguided and cannot be sustained. And this is because, if other theoretical properties make a difference to the application of a particular theory, then the observational consequences of that theory cannot be assumed to obtain in any instance without provisos about other theoretical properties beyond those specified by the theory, which requires separate investigation on the basis of observation, measurement, and experiment. The conditions for testing, confirming or falsifying alternative hypotheses and theories is thereby rendered vastly more complex than had previously been supposed. Strikingly, as an essential element of an adequate explanation, Coffa (1973) had advanced “extremal clauses” that assert that no factors other than those specified by the initial conditions of the explanans are relevant to the occurrence of the explanandum event. Indeed, Salmon points out that, since the application of every law involves a tacit extremal (or “ceteris paribus”) clause, any law can be protected from refutation by discounting disconfirming evidence on the expedient of claiming that, because the clause was not satisfied, the law is still correct, which is another way to accent the source of Hempel’s concern (Salmon 1989: 84–85).