Barrow, G. W. S. (1979). "The Idea of Freedom in Late Medieval Scotland". The Innes Review. 30 (30): 16–34. doi:10.3366/inr.1979.30.30.16. (Reprinted in G. W. S. Barrow, Scotland and its Neighbours in the Middle Ages (London, Hambledon, 1992), chapter 1