The current article studies the acquisition of the indefinite past in learning Modern Greek as a foreign language by Catalan/Spanish learners. More specifically, a contrastive analysis of Greek, Spanish and Catalan grammar takes place in order to present the conceptualization and the construction of the past tense in the three languages and the difficulties encountered by learners of Greek. Within this framework, the study examines opposing theories (i.e. the Single Mechanism Account and the Dual Mechanism Account). The authors argue in favor of the phenomenon of overgeneralization of forms. In particular, through their empirical study they attempt to show that the past tense inflection is acquired slowly taking into account the semantic and phonological content; something that indicates a single, integrated mechanism for regular and irregular forms.