2. The method of claim 1 , wherein determining the candidate word further comprises: determining, by the computing device, a group of one or more alignment points traversed by the particular portion of the gesture; determining, by the computing device, respective cost values for each of at least two keys of the plurality of keys, wherein each of the respective cost values represents a respective probability that a respective alignment point of the group of alignment points indicates a respective key of the plurality of keys; updating, by the computing device and based at least in part on at least one of the respective cost values for one or more of the at least two keys, the cost value associated with the at least one of the plurality of letter chains; and comparing, by the computing device, the respective combined cost values respectively associated with the plurality of letter chains to select the candidate word for outputting for display.
4. The method of claim 2 , wherein determining the respective cost values for each of the at least two keys of the plurality of keys comprises: determining respective physical cost values for each of the at least two keys of the plurality of keys, wherein each of the respective physical cost values represents a probability that at least one physical feature of an alignment point of the group of alignment points indicates at least one physical feature of a key of the plurality of keys; determining respective lexical cost values for each of the at least two keys of the plurality of keys, wherein each of the respective lexical cost values represents a probability that a character represented by a key of the plurality of keys is included in the candidate word; and determining, based at least in part on the respective physical cost values and the respective lexical cost values, the respective cost values for each of the at least two keys of the plurality of keys.