These errors on in-vocabulary terms can be explained by inconsistencies in annotation across the two domains: • In the PPCEME, to may be tagged as either infinitival (to, e.g., I am going to study) or as a preposition (p, e.g., I am going to Italy).
as a secondary evaluation, we measure performance on the full PTB tagset in Table 3, thereby enabling direct comparison with prior work (Yang and Eisenstein, 2016).