A theory of harmony plays a determinant role in the epistemology of tonal structure in music of the common practice, a fact that Schenkerian tonal theorists have long struggled to account for because of the polemical denials issued by Heinrich Schenker regarding the role that harmonic concepts derived from Rameau play in his theoretical frameworks (Schenker [1930] 2014). Attempts have been made recently to rectify the incongruity between Schenker’s uncompromisingly monist musical philosophy and the often-unspoken harmonic premises his ideas rely on (Yust 2015, 2018), but many aspects of how theories of functional harmony relate to the hierarchical structuration of musical time through prolongational processes remain undefined and underexamined. In this thesis, I fill in the lacuna of harmonic accounts in post-Schenkerian frameworks of tonal structure through Harmonic Regional Theory, which defines tonal harmonic process as a containment hierarchy of timespans. Using this framework, I outline a discovery process for properties of tonal stability (Yust 2018, 32) possessed by events and prolongational processes that understands these qualities as the product of stabilizing “forces” (Larson 2012) propagated by the structural influence harmonic-regional “fields” (Quinn 2020). The result is an epistemic model with tremendous analytical utility in both formal and informal analyses of tonal structure, the proof-of-concept for which is provided through the implementation of harmonic-regional theory in an automated analysis of tonal-melodic structure in Beethoven, op. 13, ii.