If we assume all derivations licensed by our grammar are equally likely, and that lexical category assignments are conditionally independent given the sentence, we can compute the optimal parseŷ as: As discussed in Section 2.1, many derivations are possible given a sequence of lexical categories, some of which may be semantically distinct.
performance was much worse, with an F-score of 79.63% on the 97.8% of sentences it parsed on CCGBank Section 23.