The allocutive su merced ‘His Grace, His Worship’ is currently regarded as a syntactic Americanism. In certain Hispanic American geolects, su merced is currently used for second person singular (2P su merced) deixis and may denote respect (V address) as well as intimacy (T address). The traditional hypothesis argues that these uses are only found in American Spanish, and that the allocutive su merced dates back to the Afro-Hispanic varieties of the colonial period. This chapter establishes, for the first time, the evolutionary connections of the current Americanism with the history of su merced usage in Spain. It also explores a new, non-literary database and argues for a new diachronic hypothesis on (2P) su merced, from a Pan-Hispanic perspective.