Abstract: The insight behind TSIM theory is that we should take at face value the view of belief, knowledge, (cognitive) information, but also of other notions less explored in formal logic, like imagination and mental simulation, as (propositional) representational mental states bearing intentionality, that is, being about states of affairs, issues, situations, or circumstances which make for their contents. I will generically call these things topics, and provide a simple formal mereology for them. The semantics for our TSIMs will be given in a kind of conditional logic framework, with an added mereology of topics.