Inertial Behavior and Generalized Partition

We call behavior inertial if it does not react to the apparent arrival of relevant information. In a context where the precise information content of signals is subjective, we formulate an axiom that captures inertial behavior, and provide a representation that explains such behavior as that of a rational decision maker who perceives a particular type of information structure, which we call a generalized partition. We characterize the learning processes that can be described by a generalized partition. We proceed to assume that there is a true underlying information structure that may not be a generalized partition, and investigate different channels that may lead the decision maker to nonetheless perceive a generalized partition (and thus to display inertial behavior): A cognitive bias referred to as cognitive inertia and a bound on rationality which we term shortsightedness.