We develop and evaluate a preliminary belief-updating model which links intermediate-term (i.e., over several days) syntactic adaptation to the joint statistics of syntactic structures and lexical cues to those structures. This model shows how subjects differentially depend on different cues to syntactic structure following changes in the reliability of those cues, as shown by Fine and Jaeger (2011). By relating syntactic adaptation and cue combination to rational inference under uncertainty, this work links learning and adaptation in sentence processing with adaptation in speech perception and non-linguistic domains.