Peircian semiotics has retained a place in the study of music for more that forty years. Few studies, however, have focused upon arguably the most important aspects of Peirce’s thought: his contribution to logic and his development of a pragmatic approach to epistemology. This article develops a theory of Peircian semiotics in music that is rigorously derived from the key insights Peirce offered philosophy. It focuses upon his theory of the proposition and posits an approach to music analysis that is sensitive to the importance of music’s internal structure while recognizing the enormously significant role played by cultural contexts and social forces in the development of musical meanings. The article introduces Peircian semiotics and develops a theory of musical valency with particular reference to the Allegro of Mozart’s ‘Prague’ symphony. It concludes by theorizing the role of cultural and ideological forces in articulating and saturating a music’s valency.