Here's a breakdown of its evolution:
1. "Vuestra merced": This phrase was originally used as a respectful title of address, similar to "Your Excellency" or "Your Highness". It was used to show deference to someone of higher social standing.
2. "Vuestra merced" shortened to "merced": Over time, the phrase was shortened to just "merced," which still carried the meaning of respect and deference.
3. "Merced" shifted to "usted": Through a process called aphesis, the initial "m" sound of "merced" was dropped, leaving "usted". This shift happened around the 15th century.
4. "Usted" became the standard form of polite address: By the 16th century, "usted" had become the standard polite pronoun in Spanish, used for addressing someone formally or as a sign of respect, regardless of their social status.
So, "usted" is essentially a shortened and transformed form of "vuestra merced," reflecting the historical evolution of respectful address in Spanish.