The purpose of this study is to show that when we treat vowel nasalization and degemination with coalescence, constraint-based approaches can be explained better than rule-based approaches from the comparison of two phonological approaches. For vowel nasalization I first analyze it by applying a nasalization and a nasal deletion rule in sequence, and then a transformational rule, but these are still inadequate from the viewpoint of coalescence and also can’t capture the functional unity of rules. Instead I can explain this nasalization appropriately by using constraints and setting a new constraint, which blocks the nasalized vowel plus nasal consonant sequence. For degemination, first I analyze it by using the assimilation rule and cluster simplification and then the transformational rule, but all are unsatisfactory in explaining degemination as coalescence. Therefore I can analyze it by using some related constraints and making a new constraint, which is driven by the necessity of accounting for the assimilation of the given examples. As the result, I can explain degemination more concisely and consistently than can rule-based approaches. (Chonnam National University)