When do native speakers say I’m glad that you like it, and when do they drop the complementizer and simply say I’m glad you like it? The factors influencing complementizer realization have intrigued many researchers over the last few decades. The emerging consensus is that various factors jointly determine whether the complementizer is realized, such as how long or complex the parts are that the complementizer connects or how frequent the verb is in actual language use. This study elaborated on previous studies by asking: what about non-native speakers of English? The “rules” for complementizer variation are never taught in the English language classroom, and yet second language learners, at least at an advanced level of proficiency, also drop the complementizer in specific contexts. We wanted to know: are these contexts the same as for native speakers? That is, do the same factors that govern native speakers’ choices also impact learners’ choices?
To that end, we retrieved 3,622 instances of complement constructions from native English corpora and German as well as Spanish learner English corpora. We coded all instances for the factors proposed in previous research and ran a logistic regression model. Our final model suggests that advanced-level learners of English are in fact closely aligned with native speakers in that their choices are, generally speaking, influenced by the same factors. However, a closer look reveals that the relative importance of these factors differs: learners rely more on processing-related factors such as clause complexity, and they are comparatively less sensitive to the statistical associations between a given verb and the complementizer. Overall, learners realize the complementizer more often in contexts in which a native speaker may well omit it. Also, comparing the German and the Spanish learners, we observed that the German speakers make more native-like choices than their Spanish peers. We interpret these findings to reflect (i) the comparatively higher cognitive cost associated with deploying your second language vs. your first, (ii) that second language learning will vary as a function of the first language the learner speaks, and (iii) the crucial role that the input learners receive plays in learning to make native-like choices.