The definitions of the basic concepts, rules, and constraints of centering theory involve underspecified notions such as ‘previous utterance’, ‘realization’, and ‘ranking’. We attempted to find the best way of defining each such notion among those that can be annotated reliably, and using a corpus of texts in two domains of practical interest. Our main result is that trying to reduce the number of utterances without a backwardlooking center (CB) results in an increased number of cases in which some discourse entity, but not the CB, gets pronominalized, and viceversa. the claim that if any discourse entity is pronominalized,.
