Is there any important distinction between a law and a theory? Some usages suggest that there is. Thus, everyone speaks of Boyle's Law (not theory) and of the dynamical theory (not law or laws) of gases. But the most summary inquiry will show that the distinction is not maintained consistently by individual authors, still less as between different authors; the terms “Newtonian law” and “theory of gravitation” seem to be used indifferently to denote the same proposition(s).