Even historical developments which appear opaque due to limited empirical data may prove tractable when sources of diverse types are combined. For systems of three-way inflectional contrast among imperfect indicative forms in a geographically coherent cluster of Catalan, Aragonese and Gascon varieties (e.g. first-conjugation [kanˈtaβam] ‘we sang’; third-conjugation [peɾˈðeβam] ‘we lost’; fourth-conjugation [paˈtiβam] ‘we suffered’ in the Catalan variety of Castigaleu), two principal accounts have been proposed: an ‘etymological’ hypothesis in which three-way imperfect contrasts represent a conservative feature continuing Latin forms, and an ‘analogical’ hypothesis in which thematic labials in non-first-conjugation imperfects are ascribed to analogical innovation. By examining historical texts, modern dialect data and areal patterns in order to develop a unified analysis of the Pyrenean systems, this study demonstrates that the modern systems result from analogical innovation, and further establishes the directionality and relative chronology of the analogical changes involved.