Unforeseen Contingencies ∗

We develop a model of unforeseen contingencies. These are contingencies that are understood by economic agents — their consequences and probabilities are known — but are such that every description of such events necessarily leaves out relevant features that have a non-negligible impact on the parties’ expected utilities. Using a simple co-insurance problem as backdrop, we introduce a model where states are described in terms of objective features, and the description of an event specifies a finite number of such features. In this setting, unforeseen contingencies are present in the co-insurance problem when the first-best risk-sharing contract varies with the states of nature in a complex way that makes it highly sensitive to the component features of the states. In this environment, although agents can compute expected payoffs, they are unable to include in any ex-ante agreement a description of the relevant contingencies that captures (even approximately) the relevant complexity of the risky environment. JEL Classification: C69, D81, D89.