Current psychological accounts of causal representation and reasoning do not capture phenomena related to causation by omission (e.g., “The absence of breathing causes death”), with one exception (Wolff, Barbey, & Hausknecht, 2010). We describe a novel theory of omissive causation that posits that people build discrete mental simulations – mental models – of causal relations (Goldvarg & Johnson-Laird 2001). The theory states that causes by omission refer to a set of temporally ordered models of possibilities. Reasoners tend to focus on only one of those models, i.e., the possibility in which breathing does not occur and death subsequently does. Likewise, the theory posits that reasoners distinguish between omission in the context of causation, enabling conditions, and prevention. We describe some initial predictions made by the model-based account, contrast it with an alternative psychological theory based on the transmission of causal forces, and set out directions for further research.