 This observation suggests a way to specify which causes of “X” determine its content. The content of “X”, say, the firing of some neurons, is determined by dogs, and not foxes, because it is the function of those neurons to register the presence of dogs, but not foxes. Further, the content of “X” does not include LSD, microelectrodes, or quantum mechanical fluctuations, because it is not the function of “X” to fire in response to LSD, microelectrodes, or quantum mechanical fluctuations in the brain. Similarly, the content of “X” does not include proximal sensory projections of dogs, because the function of the neurons is to register the presence of the dogs, not the sensory stimulations. It is the objective features of the world that matter to an organism, not its sensory states. Finally, it is the function of “X” to register the presence of dogs, but not the presence of questions, such as ‘What kind of animal is named  “Fido”?’, that leads to “X” meaning dogs. Functions, thus, provide a prima facie attractive means of properly winnowing down the causes of “X” to those that are genuinely content determining.