xxiii, 507 p. / This dissertation contextualizes melodic variation within a cultural, historical, and cognitive framework. This work discusses how traditional musicians learn how to vary melodies by observing norms of social and musical behavior exhibited by senior musicians. The core of this dissertation is the transcription and analysis of fifty source recordings of fifty different Irish musicians playing one tune each dating from between 1904 and 2007. Though the transcriptions of the recordings exhibited a high instance of melodic variation (48.2% of the measures), only a small percentage of variation fell on set accented tones (an average of 7.3%). The considerable invariance of set accented tones suggests that part of what constitutes the concept of a tune in an Irish musician's mind relates to the pitch of these key tones. I introduce the term aesthetic conservatism to designate a philosophical approach to performance practice that seeks to maintain both the dance genre and tune identity. I argue that aesthetic conservatism may be a by-product of archetypes and exemplars created through transcriptions and recording technology. This conservatism may also be a function of famine-induced fear of cultural dissolution or inferiority with respect to more prominent music-making supercultures. I call on the philosophy of aesthetic conservatism to explain why few set accented tones are varied. Of the measures that were varied, 74% of those variations involved the addition, subtraction, or redistribution of ornamentation. To catalogue the variety of variations within this sample, I propose a taxonomy that is designed to account for the number of notes in a measure and to assess intervallic differences over successive repetitions of a tune. Finally, I propose a theory to explain the cognitive processes that allow a musician to vary a melody. I suggest that in the mind of a traditional musician there is both a tune schema and a variation schema. These are flexible models that are distinct and separate but that interact within a short span of time because of the exceptionally efficient anatomy of a musician's brain. / Committee in charge: Anne Dhu McLucas, Chairperson; Lori Kruckenberg, Member; Stephen Rodgers, Member; Glen Waddell, Outside Member