This study aims to examine the changes of three different levels that appear in the modern Korean language, especially the changes of second type, ‘-느-’. The second type, ‘-느-’, of modern Korean language appears in the expressions such as ‘-느냐’, ‘-는데’, ‘-는가’ and ‘-는지,’ and it normally has limitations in the combination with adjectives, but it can freely be combined with the past tense expression of ‘-었-’, unlike the ‘-느-’ in ‘-는 다’ and ‘-는구나’. In particular, it is noted that the word structure including the second type of ‘-느-’ is always an integrated ending including the adnominal ending ‘-ㄴ’. The reason why the second type, ‘-느-’, appears in the integrated ending inclusive of adnominal ending due to the limitations that originate from the prefinal ending ‘-□-’. A stage by stagy review of data on ancient Korean language has proven the high tendency of ‘-□-’ to be combined with adnominal ending from the olden times. Because of the characteristics of ‘-□-’ combining with adnominal ending, the limitations such as ‘-□-+-ㄴ’ were created and because of those limitations, the structure of ‘잇-+-□-+-ㄴ(X)’ in the Middle Age Korean could be drawn. And in the process of contracting the expression ‘-어 잇-’ into ‘-엇-’, the change of ‘-어 잇□+(ㄴ) > 엇□(ㄴ)’ happened which resulted in the combination of ‘-었는데, -었는가, -었느냐’ in modern Korean.