The connective 'but' mainly represents two different contrastive relations (Lakoff, 1971; Van Dijk, 1979; Blakemore, 1989). One of them is semantic, which shows semantic opposition and where no expectation is denied. The other is pragmatic, which shows a denial of expectation. This study aimed to investigate the use of 'but' by Turkish EFL students in their L2 writings in terms of the relations it indicated. The participants of the study were the first-year students in the Department of English Language and Literature in Hatay Mustafa Kemal University in Turkey. Students' argumentative essays written in the Research and Study Techniques course were used for the study. Each instance of 'but' was coded based on the relation it indicated, and then those relations were separated into categories depending on their meaning in the context. The findings showed that the number of pragmatic uses was higher than semantic uses in the students' L2 writings and that the pragmatic uses could be categorized as violated expectation, correction, evidence, and emphasizing condition. The study revealed that L1 transfer, frequency in the L2 input, context, position of the connective 'but' in the sentence, and the type of the essay were related to the use of semantic or pragmatic contrast. The study also revealed that the unmarked function of 'but' could be violated expectations.