The Challenges of a Syntactic Category It is a long-standing question in theoretical linguistics what makes up a specific syntactic category (e.g. Brown & Miller 1991, Carnie 2007): e.g. position in a sentence or semantic content. For example, if adjectives are words describing a quality, then why is "courage" not an adjective? This study investigates the common mistakes of the misuse of parts of speech made by ESL learners and attempts to identify the linguistic patterns of that misuse. The results of a pilot study (e.g. free writing) suggest that the most common mistakes are the cases that are puzzling even for theoretical linguists: syntactic position versus meaning. This preliminary study identified several syntactic contexts in which students are prone to mistakes: e.g. position of a complement of a verb, of a preposition and of a noun. If a syntactic context allows for several parts of speech (noun, gerund and verb: e.g. to a response, to responding, to respond), learners are likely to take the content of the word (e.g. action) as an indicative clue to decide on the choice of the part of speech. This research studies the correlation of the linguistic components (e.g. syntactic position, semantic content, morphological complexity, syntactic context) of such patterns of misuse in a variety of contexts: matrix and embedded clauses. References: Brown, K. and J. Miller. 1991. Syntax: A linguistic introduction to sentence structure, 2nd edition. London: UK: HarperCollins Academic. Carnie, A. 2007. Syntax: A generative introduction, 2nd edition. Malden, MA: Blackwell Publishing.