One of the central problems in cognitive science concerns our ability to understand others in terms of mental state attribution. We, humans, think of each other as having minds, an assumption which indeed forms the basis of our daily communication: by attributing mental state we understand and predict each other’s behavior. But what mechanisms underpin this ability? This is a question that has preoccupied philosophers and cognitive scientists for more than four decades. In this paper, I will examine two dominant (...) solutions, Theory-Theory and Simulation-Theory, to this question. In section one, I distinguish between two different senses of "theory" and cite considerable evidence in favor of the modular version of Theory-Theory. In section two, after introducing Simulation Theory as an alternative to Theory-Theory, I distinguish between three possible senses of "similarity" in simulation, argue that none of them are free from certain difficulties. (shrink)