Between 1450 and 1520 there were frequent uprisings in England and Castile, many directed at royal councilors, a few aimed at monarchs themselves, but nearly all claiming to seek some sort of reform. They occurred during a period of critical development for political thought in Western Europe. Languages and ideas that previously had belonged to the realm of philosophical thought moved into the world of operative politics, taken up by a broad contingent of subjects and citizens demanding accountability, good government, and, occasionally, inclusion in the legislative process. The ideas under consideration in this dissertation are: the political kingdom; the common weal, res publica, cosa pública, and buen público; conciliarism and the corpus mysticum; and historical precedent. The same languages of legitimacy and representation were used in Castile and England. However, in Castile these languages were contested by a discourse of kingship that permitted no limitation, real or theoretical, on the king’s auctoritas. This and the failure to fully implement the aforementioned languages in operative discourse ultimately hindered participation of Cortes and community in the life of the kingdom. It also explains why the Cortes found it difficult to assert itself, and the community found it even more difficult to reform royal government, including the Cortes. In England, discourses of royal authority were far less developed and successful than in Castile. Subjects integrated into the development of the state in England because they had recourse to languages of communal representation and civic participation that validated their involvement in the political community. Englishmen identified Parliament as the legitimate forum for channeling communal discontent or desires. The legitimacy Parliament achieved in this period remained with the body. This was due in large part to the strength of the languages used to legitimate Parliament, and their continued presence in English discourse.