1. A method implemented by a system of one or more computers, comprising: receiving, at the system, text to be synthesized as a spoken utterance; analyzing, by the system, the received text to determine attributes of the received text; selecting, by the system, one or more candidate utterances from a database of stored utterances based on a comparison between the determined attributes of the received text and corresponding attributes of text representing the stored utterances; determining, by the system for each candidate utterance, a distance between a prosodic contour of the candidate utterance and a hypothetical prosodic contour of the spoken utterance to be synthesized, the determination based on a model that relates a) distances between prosodic contours of pairs of the stored utterances to b) relationships between attributes of text of each of the respective pairs, wherein the model is embodied by information including, for each of the stored utterances: a prosodic contour of the respective stored utterance, one or more attributes of text of the respective stored utterance, and first data relating a difference between the prosodic contour of the respective stored utterance to the prosodic contour of a second stored utterance to a difference between a first attribute of the text of the respective stored utterance and the first attribute of the text of the second stored utterance, second data relating a difference between the prosodic contour of the respective stored utterance to the prosodic contour of a third stored utterance to a difference between the first attribute of the text of the respective stored utterance and the first attribute of the text of the third stored utterance, wherein the second stored utterance and the third stored utterance are in the stored utterances, and wherein prosodic contours represent prosodic characteristics of speech at different times; selecting, by the system, a final candidate utterance having a prosodic contour with a closest distance to the hypothetical prosodic contour; and generating, by the system, a prosodic contour for the text to be synthesized based on the contour of the final candidate utterance.