The purpose of this study is to investigate geminates, classify them into assimilated geminates and concatenated ones, and analyze them in phonologically different aspects. For the assimilated geminates cases, first we consider previous approaches, such as rule-based analyses, coalescence, and ambisyllabicity with their comparisons, but these methods cannot account for the motivation of deletion of a consonant in gemination occurring after assimilation. Therefore, as an alternative to these analyses, we adopt a constraint-based approach to account for them clearly. On the other hand, for the concatenated geminates, we propose the different idea that the gemination is not shortening by degemination, but rather lengthening effects by assimilation and it can be explained appropriately more in moraic representation than in other approaches. As a way of proving this, we research and examine the duration of a geminate and a singleton in acoustic aspects. Finally, as was supposed, we can confirm the fact that the results of experimental studies regarding the duration of geminated consonants show that they are much longer than just their singleton counterparts. In addition, when we teach students English pronunciation, this may be a cue to refer to as useful information.