The present paper provides a contemporary viewpoint of phonological representations. Specifically, I present contrastive hierarchies of distinctive features adopting the Modified Contrastive Specification (MCS, Dresher, Piggott and Rice 1994, Dresher 2008, 2009) and the dimension hypothesis (Avery and Idsardi 2001, Purnell, Raimy and Salmons 2018). Under these frameworks, I reanalyze and revise Ko's (2009) proposals on the contrastive hierarchies of Korean vowels. The two-step merger of a low back vowel from Late Middle Korean to Early Modern Korean exemplifies how the modified hierarchies can provide a more efficient and systematic account. As for synchronic examples, I illustrate a merger of a low high front and a mid high front vowel and a feature unpacking phenomenon of high front rounded vowels under the proposed hierarchies. Furthermore, Oxford's (2015) model for sound change is applied to evaluate the revised representations. The diachronic and synchronic sound change data are well verified by his model. I argue that the representations proposed in this study hold their advantages as they offer more economical and consistent explanations for sound changes.