This study examined the ways in which teachers of English as a second language (ESL) perceive the semantic and syntactic constraints that govern word use and the strategies they use to explain lexical anomalies to students. Twelve native speaking ESL teachers from 2 university-level intensive English programs were asked to identify, categorize, and explain lexical anomalies in each of 14 sentences. It was found that 3 teachers did not identify any categories for any of the 14 anomalies and that 7 teachers categorized fewer than 4 of the anomalies. The label that was most frequently used was "connotation," while only one teacher used "collocation," a basic term in lexical research, to categorize inappropriate idiomatic usage. The results of this study indicate that certain categories of inappropriate usage, especially animate/inanimate collocations and positive/negative collocations, are fairly transparent to ESL teachers. Although teachers did not consistently identify lexical categories, their explanations revealed considerable insight into what limits word use in these categories. The explanation strategy of illustrating word meaning by showing the relations between two or more words and by giving examples were often used appropriately in spite of inappropriate categorizations. (MDM)