This research aims to fill the gap about the 18th and 19th- Spanish and Portuguese spoken in the Iberian Peninsula, by analysing the emergence and development of their own pragmatic system in forms of address. Both languages underwent deep changes from 1700’s onwards, but these have been hardly researched although some of them affected both sides of the Atlantic. This project attempts to shed light on the arising of a politeness pronouns system that is only attested in the south-western part of the Peninsula and which does not follow the standard or any other system elsewhere in Spain and Portugal. By collecting private correspondence and juridical documents that show real language use, this investigation intends to find why this phenomenon emerged in the south-west, what type of speaker prompted or disfavoured it, what evolution it underwent until establishing itself and what linguistic behaviour it has been characterised by. Likewise, the study of this feature may also underpin the theory about a Sprachbund formed in the south-western Iberian Peninsula between Spanish and Portuguese and how its relation with America prompted common linguistic developments in both the European and American varieties. This study represents pioneering research, since more and more authors are drawing attention to the importance of the 18th and 19th centuries as turning points in the evolution of Spanish and Portuguese, and how these centuries can help understand the current state of both languages and the differences witnessed not only on both sides of the Atlantic, but also within the Iberian Peninsula.