Bumke Joachim. The Concept of Knighthood in the Middle Ages

New York: Ams Press, 1982. — 268 p.This book to definitively explain the concept of knighthood in the Middle Ages. It's a translation of a German work, for one thing, so it's really more specifically about the concept of knighthood in the Germanic world in the Middle Ages, arguing from the meaning of various technical terms in early Germanic dialects. And from what I can tell, the author is arguing against the existence of a coherent "concept of knighthood" - terms that later meant knighthood as an enterprise for nobles and kings were used in earlier ages for mercenaries and unfree soldiers.