This study investigates the use of high-frequency cognitive verbs - think and believe - in Turkish L2 learners' interlanguage, both in terms of their verb senses and complementation patterns. In line with this purpose, a Sentence Production Task consisting of context-independent items and a Sentence Completion Task consisting of context-dependent items were developed by using the Corpus of Contemporary American English (COCA). These tasks were applied to 182 students at four different vocabulary levels. The findings indicated that the learners showed a strong tendency to use verb think in the verb sense of expressing a personal opinion and in the complementation pattern of [zero that-CL]. Along with these results, the acceptability levels of learners' productions with the verbs think and believe showed differences. The learners had problems with the use of believe more than they had with the verb think. The findings have pedagogical implications by shedding light on the learner preferences for verb complementation patterns and senses. The findings also provide an insight into the learners' performance on the syntactic and semantic properties of the cognitive verbs through context-dependent and independent tasks.