 For the most part, philosophers have thought that if scientists have discovered any exceptionless regularities that are laws, they have done so at the level of fundamental physics. A few philosophers, however, are doubtful that there are exceptionless regularities at even this basic level. For example, Cartwright has argued that the descriptive and the explanatory aspects of laws conflict. “Rendered as descriptions of fact, they are false; amended to be true, they lose their fundamental explanatory force” (1980, 75). Consider Newton’s gravitational principle, F = Gmm′/r2. Properly understood, according to Cartwright, it says that for any two bodies the force between them is Gmm′/r2. But if that is what the law says then the law is not an exceptionless regularity. This is because the force between two bodies is influenced by other properties than just their mass and the distance between them, by properties like the charge of the two bodies as described by Coulomb’s law. The statement of the gravitational principle can be amended to make it true, but that, according to Cartwright, at least on certain standard ways of doing so, would strip it of its explanatory power. For example, if the principle is taken to hold only that F = Gmm′/r2 if there are no forces other than gravitational forces at work, then though it would be true it would not apply except in idealized circumstances. Lange (1993) uses a different example to make a similar point. Consider a standard expression of the law of thermal expansion: ‘Whenever the temperature of a metal bar of length L0 changes by T, the length of the bar changes by L = kL0T,’ where k is a constant, the thermal expansion coefficient of the metal. If this expression were used to express the strict generalization straightforwardly suggested by its grammar, then such an utterance would be false since the length of a bar does not change in the way described in cases where someone is hammering on the ends of the bar. It looks like the law will require provisos, but so many that the only apparent way of taking into consideration all the required provisos would be with something like a ceteris-paribus clause. Then the concern becomes that the statement would be empty. Because of the difficulty of stating plausible truth conditions for ceteris-paribus sentences, it is feared that ‘Other things being equal, L = kL0T’ could only mean ‘L = kL0T provided that L = kL0T.’