Multiparty parliamentary democracies present an interesting problem to voters: in order to cast a policy-oriented vote, they must first come to have some expectations of how likely various coalition governments are to form following the election. While there is some research suggesting that voters do, in fact, possess such expectations, it is unclear how they are generated. We present an ecologically rational theory of how voters form coalition expectations and derive global and contextual (i.e., cross-nationally variant) empirical expectations. To test these predictions, we design an experimental platform that allows us to learn the rules voters use to infer which parties will coalesce, as well as how these rules vary across contexts.