merchant would be considered a member of the middle class in a Medieval society.
The Medieval society was complex, and was not so far away from what we would call a modern one. It was governed by laws, it had rules, the people had rights and obligations. There was a legal framework of land tenure, taxation and fiscal immunities. There was an urban organization and a rural one. The Feudal system had laws regarding the relationship between lords and peasants, and between the seigneurs and the monarch