Language norms are dynamic conventions that change over time. In the case of Catalan, the 20th century represents a critical codification period. In this paper, the author discusses the influence of internal and external factors on the evolution of four connectives mainly used in formal (written) communication (nogensmenys ‘nonetheless’, emperò ‘but’, no obstant (això) ‘nevertheless’ and tanmateix ‘however’), which have experienced remarkable change during the 20th century. Three sources of information are considered: dictionaries, grammars, and corpus examples (from Corpus Textual Informatitzat de la Llengua Catalana) in the period 1904–2013. The review of dictionaries and grammars shows that descriptions and norms change over time. The corpus reveals the impact of prescription on the use of the connectives in formal registers. The basic research question asks: to what extent do linguistic and socio-cultural factors have an influence on change in the field of connectives and how do norms and formal use interact? The analysis shows that external factors (i.e., bilingual context and codification processes) in correlation with internal ones (i.e., paradigmatic relations) affect both linguistic change and norm change. The evolution of the four connectives analyzed is the result of a changing language norm forbidding or encouraging the use of certain forms, almost always triggered by an intent to compensate for the influence of the dominant language, Spanish.