Optimality, Belief and Preference Dick de Jongh, Fenrong Liu Abstract: We define preference in terms of a constraint sequence, a concept from optimality theory. In case agents only have incomplete information, beliefs are introduced. We propose three definitions to describe dierent procedures agents may follow to get a preference relation using the incomplete information. Changes of preference are explored w.r.t their sources: changes of the constraint sequence, and changes in beliefs. Keywords: Optimality; Preference; Belief; Constraint sequence