<i>Al hablar, se alterna hablando</i>
This paper adresses the possible relationship between synchronic variation and diachronic change. It will be argued that the existence of contexts in which both alternating forms may occur without hindering the communicative inferences of the intended message should eventually favour the alternative that has some (communicative and/or formal) advantage over the other and cause a shift towards this form over time. The example that illustrates this hypothesis is the alternation between two Spanish non-finite constructions <i>al</i> + infinitive and <i>gerundio</i>. The purpose of this paper is to demonstrate that these so-called fuzzy contexts, necessary for linguistic change, actually exist.