Investigating Optional Functional Element and Obligatory Contour Principle in L2 Comprehension and Production Among ESL Learners

Most studies in optional functional element (OFE), specifically the optional function word (OFW) such as the optional that and obligatory contour principle (OCP),are concerned with accounting facilitation in language production in L1. The present study accounted for comprehension facilitation of OFE and OCP in syntactically ambiguous clausal complement, and OCP in L2 production among 180 ESL speakers. Utilizing quasi-experimental through the nonequivalent groups research design, the study found out differences in the interpretation of sentences with and without that. Adjacent identical elements (double thats) seemed to be avoided because they are perceived to be ungrammatical. Findings suggest that complementary clause (CC), with an embedded specific noun, is easily understood if optional that is included, whereas CC with an embedded common noun is easily understood without the said optional word. Findings are also pivotal in understanding comprehension-facilitation and production-facilitation accounts in L2 with respect to OFE and OCP.