The predictive powers of fine-grained syntactic complexity indices for letter writing proficiency and their relationship to pragmatic appropriateness

Drawing on 300 request letters and 300 self-recommendation letters composed by Chinese adolescent English as a foreign language (EFL) learners in the National Matriculation English Test, this study investigated the predictive powers of 10 fine-grained syntactic complexity (SC) indices related to dependent clause (DC) and complex noun phrase (CNP) usage for rated proficiency levels of these two types of letters. We further examined the connection between significant SC predictors for proficiency ratings and differential degrees of politeness and formality among these letters rated at different proficiency levels. The results revealed that in both types of letters, the clausal and noun phrase features associated with the fine-grained DC- and CNP-related indices predictive of the rated proficiency levels of these letters reflect the varied degrees of politeness and formality with which learners of different English writing proficiency used different syntactic patterns to perform requests and self-recommendations in letter writing. Our findings have important implications for understanding the functional values of SC for facilitating appropriate and effective communication in EFL learners' letter writing.