Speaker Series: Dr. Juhani Yli-Vakkuri, University of Oslo "Mirror Thoughts"

Short Abstract: Let the qualitative agential profile of a thought be the strongest qualitative intrinsic property of the system consisting of the thought and the agent who thinks it. Thus, e.g., the qualitative agential profile of the thought you express by ‘Water is wet’ is the same as that of the corresponding thought your doppelganger on Twin Earth expresses by the same (or sound-alike) words. One natural thought about narrow content is that, if there is such a thing as narrow content, then, necessarily, the narrow contents of thoughts with the same qualitative agential profile are the same. Another natural thought about narrow content is that (the first thought is true and) a priority supervenes on narrow content (or at least on narrow content plus logical form): if so, then, necessarily, whenever two thoughts have the same qualitative agential profile (or have the same logical form plus corresponding constituents with the same qualitative agential profiles), one is a priori if and only if the other is. The possibility of mirror thoughts--two or more distinct thoughts of the same agent that have the same qualitative agential profile--make trouble for both claims. First, if mirror thoughts are possible and the first thought is true, then the truth values of the narrow contents of our thoughts must vary with some very exotic parameters (the usual centered-worlds machinery of world-agent-time triples, or even world-agent-time-location quadruples, cannot handle them). Second, if mirror thoughts are possible, then the second thought is false.