This project aims at understanding which functional categories are predicted to be expletive in natural languages according to the hypothesis that, despite making no semantic contribution to linguistic meaning, they convey expressive meanings beyond grammar. Therefore, this project pursues an important theoretical contribution in connection to what can be considered an expletive category in Universal Grammar, grounded on the minimalist program on Generative Grammar, on formal semantics and on a Semantic Commitment model of the syntax-pragmatics interface. We aim to cover both synchronic and diachronic studies, which will foster our knowledge of what is a good candidate for an expletive category, and what are the potential changes that a linguistic item may have to undergo to change into an expletive item. The present project also has an experimental perspective by introducing elicitation work and corpus work. We will collect data in spoken and written modalities of natural languages by using a variety of psycholinguistic methods to investigate whether the presence of different types of expletives affects the processing of linguistic sequences. We also aim to understand the extent to which expletive items are optional and redundant both during comprehension and production. Corpora research, as we have previously done in relation to the emergence of verbal discourse markers in Spanish, will be done by accessing public corpora of the studied languages (e.g. CORPES XXI, CORDE, CICA, Davies corpora).