 Another problem arises with items or kinds that are indistinguishable. Adams and Aizawa (1994), and, implicitly, McLaughlin, (1991), among others, have discussed this problem. As one example, consider the time at which the two minerals, jadeite and nephrite, were chemically indistinguishable and were both thought to be jade. As another, one might appeal to H2O and XYZ (the stuff of philosophical thought experiments, the water look-alike substance found on twin-earth). Let X = jadeite and Y = nephrite and let there be laws ‘jadeite causes “X”’ and ‘nephrite causes “X”’. Can “X” mean jadeite? No. Condition (1) is satisfied, since it is a law that ‘jadeite causes “X”’. Condition (3) is satisfied, since breaking the jadeite-“X” law will immediately break the nephrite-“X” law. If jadeite cannot trigger an “X”, then neither can nephrite, since the two are indistinguishable. That is, there is a synchronic dependence of the ‘nephrite causes “X”’ law on the ‘jadeite causes “X” law. The problem arises with condition (2). Breaking the jadeite-“X” law will thereby break the nephrite-“X” law, but breaking the nephrite-“X” law will also thereby break the jadeite-“X” law. Condition (2) cannot be satisfied, since there is a symmetric dependence between the jadeite-“X” law and the nephrite-“X” law. By parity of reasoning, “X” cannot mean nephrite. So, can “X” mean jade? No. As before, conditions (1) and (3) could be satisfied, since there could be a jade-“X” law and the jadeite-“X” law and the nephrite-“X” law could synchronically depend on it. The problem is, again, with condition (2). Presumably breaking the jade-“X” law would break the jadeite-“X” and nephrite-“X” law, but breaking either of them would break the jade-“X” law. The problem is, again, with symmetric dependencies.