The relationship of mass composition to the study of rhetoric has occupied many writers interested in perceiving the two as analogous in organisation, vocabulary and persuasive goals. Grammar belonged to the choirboy's education but, more importantly, the method of grammar permeated the general teaching method for other subjects as well. Material, such as questions or disputations, was organised into the similar and the dissimilar, so that working from a model and transfer by analogy were the principal means of making connections between statements and ideas. This essay is concerned with the opportunities available in sixteenth-century Spain for the study of grammar and music and how these possibilities affected the leading Spanish composer of the time, Cristóbal de Morales. In this discussion, Juan Bermudo's treatise Declaración de instruments is important. Not only does it name leading humanists and composers, and present its theoretical remarks in the language of rhetoric; Morales, who had been in close contact with Bermudo at the Marchena estate of the Duke of Arcos, recommended the treatise. Thus Bermudo, a young Minorite monk, reveals a good deal about Morales by both direct quotation and analogy, and in effect provides a more rounded intellectual impression of the composer, who otherwise expressed himself only in his musical works and their dedications. It can be deduced from musical quotations that Morales is Bermudo's model composer, and by analogy that Morales, versed in rhetoric and imitation, understood the application of these rules in musical composition. In his thorough appraisal of musical tradition, theory and practice, Bermudo assumes the function of a critic in the modern sense.