 In context 2 and context 3, Oscar’s ‘water’-thoughts are about water, i.e. H2O, while in context 1 they are about XYZ. Whether Oscar’s thought about the substance in the beaker is true or not depends on two things: what his thought means, i.e. its broad content, and a certain fact about the world, namely what substance is in the beaker. Since a context includes all the objective facts about a world plus additional information about the “center” of the world, each context determines a unique possible world. For example, if we take context 1 and subtract the information about the time and individual on which the context is centered, we obtain a possible world we could call w(context 1).