Features used in the article error correction system trained discriminatively. wB and wA denote the word immediately before and after the target, respectively; and pB and pA denote the POS tag before and after the target. headW denotes the NP head. NC stands for noun compound and is active if the second to last word in the NP is tagged as a noun. Verb features are active if the NP is the direct object of a verb. Preposition features are active if the NP is immediately preceded by a preposition. Adj feature is active if the first word (or the second word preceded by an adverb) in the NP is an adjective. NpWords and npTags denote all words (POS tags) in the NP. Adapted models also use the author's article as a feature.