 One influential argument for narrow content (Fodor 1987; a recent defense of this kind of argument, with relies to criticisms, is Gaukroger, 2017) appeals to considerations involving causal explanation. We might outline the argument like this. A first premise is that mental states causally explain behavior by virtue of the content they have. Although this has been denied by some, it certainly seems to be a central part of commonsense psychology. Our behavior seems to be a causal consequence of our beliefs and desires; moreover, the content of those beliefs and desires seems to be centrally involved in the causation of behavior. We behave the way we do because of what we want and what we believe, and this seems to be just another way of saying that we behave as we do because of the contents of our beliefs and desires. A second premise is that the causal powers of an entity, its capacity to produce effects, must be intrinsic features of the entity. Thus twins, who share all their intrinsic properties, must share their causal powers. This premise seems plausible for at least two reasons. First, causation is local. It seems that features of the environment can affect an individual’s actions only by way of effects on the individual’s intrinsic properties. Second, causal powers should be evaluated across contexts. If an astronaut on the Moon can easily lift a one-hundred-kilogram weight and I, on Earth, cannot, this does not mean that the astronaut is stronger; the crucial issue is whether the astronaut can lift more than I can in the same environments. This appears to show that my Twin Earth counterpart and I have the same causal powers even though I can obtain water by turning on the faucet and he cannot, since our parallel actions will achieve parallel results provided that our environments are the same. A third and final premise is that broad content does not characterize intrinsic features, at least not essentially; thus twins need not share broad contents. According to the first premise, mental states must have a kind of content that causally explains behavior. Taken together, the second and third premises show that broad content cannot fulfill this role. The conclusion of the argument, then, is that mental states must have narrow contents, contents that are shared between twins.