 So, what function from scenarios to truth values constitutes the narrow content of my thought that the lakes contain water? Put slightly differently, which scenarios does this narrow content include and which does it exclude? To find out whether the narrow content of the thought that the lakes contain water includes a given scenario, I consider the hypothesis that the scenario is actual. For example, if I consider the hypothesis that a scenario in which the oceans and lakes around me contain H2O is actual, then I will be led by a priori reasoning to the conclusion that the lakes contain water; hence, the narrow content of my thought that the lakes contain water includes this Twin Earthly scenario. Similarly, if I consider the hypothesis that a scenario in which the oceans and lakes contain XYZ is actual, I will still conclude that the lakes contain water, since in Twin Earth scenarios my water-thoughts are about XYZ. So the Twin Earthly scenario is also included in the narrow content of my thought that the lakes contain water. By contrast, the narrow content of my thought that water is H2O will separate these two scenarios. If I consider the hypothesis that an Earthly scenario is actual, I will conclude that water is H2O, so the narrow content of the thought that water is H2O includes Earthly scenarios. However, if I consider the hypothesis that a Twin Earthly scenario is actual, I will conclude that water is not H2O (rather, it is XYZ), so the narrow content of my thought that water is H2O excludes Twin Earthly scenarios.