The subject slot is a main part of any English sentence (Martha & Robert, 2012). The recognition of the subject slot is therefore a crucial step in understanding and comprehending a sentence. This paper studies the effect of the internal structure of the subject slot on its recognition by students learning English as a foreign language (EFL). The students are given written tests containing sentences with different subject structures. Those structures vary from simple to compound-complex. The results support the main hypothesis of the study: the degree of the complexity of the structure affects the students' recognition of the subject slot of a sentence. The surprising finding of the study, however, is that a compound subject, whether simple or complex, is easier for the students to recognize than a non-compound complex subject structure. The findings of the study are intended to positively contribute to the process of teaching a language. Regarding the findings of this study, EFL instructors can draw their students' attention to the different structures of a sentence. The students need to know that some parts of the sentence are to extend or add information to the slots of the sentence but not change it.