In this study, we investigated the semantic and aspectual conditions that allow the alternation between the prepositional group with structure "a + infinitive clause" and the simple morphological construction of gerund (al escuchar- escuchando). With the tools of semantic-aspectual analysis, the structures and/or conformational mechanisms were evaluated to find the factors that motivated the alternation between the prepositional group and the morphological realization of gerund. The factors involved in the alternation are related to the lexical aspect of the predicates in which they are inserted and to the phenomena of grammatical semantic readjustments: aspectual coercion and focalization.