Whatever else may have afflicted our culture, we have in the past four hundred years greatly improved our knowledge of the workings of nature; and our knowledge of nature is such that our knowledge of particular natural causes and our knowledge of the truth of certain law-like physical or chemical generalisations are very often closely connected. If I do in fact know that on a given occasion what caused the change in the pressure exerted by a given volume of a particular gas was a change in its temperature, I do so partly in virtue of also knowing the truth of the gas law equations and perhaps also of some of the further law-like generalisations that comprise the kinetic theory. If I do in fact know the generalisations of geometrical optics to be true, it is because I and others have been able to produce specific visual effects on given occasions by making use of them. Why then should we be surprised if philosophers have tended to offer accounts of the notion of causality which link it in the most conceptually intimate ways to that of a law-like generalisation, some going so far as to make it part of the meaning of the words "cause' and "effect' and its cognates and translations that a cause and its effect are always members of classes which are linked by some law-like generalisation?