My doctoral thesis analyses the relation between Spanish and Greek language with a view to highlight their similarities and differences. This action is achieved via contrastive linguistics, sociolinguistics, and the creation of a corpus composed by 34 persons (volunteers) whose native language is Greek. Our subject focuses on the subordinate adverbial clauses regarding Spanish language and the way they have been understood and processed by those who participate in this research. The key points of this thesis are: A chapter which is provided with detailed description of the adverbial clauses in both languages showing emphasis on their common points. Moreover, we focus on mood and conjunctions for each case (each different type of clause) analyzing the grammar theory in Spanish and Greek languages. The collection of results that was achieved through a series of interviews. In each interview divided into three parts, the participants are two. During the first phase, the doctoral researcher establishes a dialogue with each one of them separately. In the second one, the participants enter a dialogue, without the researcher’s interference, and during the third and last phase, they respond to questions related to a text provided to them. There are two purposes: a. Track the cases of subordinate adverbial clauses, where either it is encountered a mistake or they constitute a worth – noticing example of correct use, having taken into consideration the participants’ answers. In two separate chapters are presented both the correct and wrong answers, and follows the analysis of the reasons that lead to the specific choices (grammatical structures). b. The social factors that affect the number of right and wrong choices (regarding grammatical structures). The variables that constitute the object of interest in this research are the following: level of knowledge in Spanish language, years dedicated to learning Spanish, studies, age, and gender. According to the results, we reach conclusions concerning the relationship of these variables as far as grade of assimilation of Spanish language is concerned (by the participants). Key words: Contrastive Linguistics, Sociolinguistics, Interview, Variables, Adverbial Subordinate Clauses