閩南語的〈入〉字頭約相當於中古〈日〉母^1，這個聲類在閩南漳泉地區主要有兩種變體j-, l-，其分界線略與漳泉方言境界競合。漳泉腔閩南語由唐山過台灣之後，先是漳音的j-佔優勢，另外g-變體也在鶴佬客分佈區崛起。然而社會方言學調查卻證明，l-已經成為台灣閩南語音變的新趨勢。不論閩南或台灣，泉音的l-都表現了強大的競爭力，顯然「入歸柳」已經是閩南語的音變「潮流」。本文目的在解明〈入〉字頭的分化、競爭與融合的過程，並以原鄉的「人口效應」、語音的「有標性效應」、音韻的「結構完整性效應」、客語「底層效應」、語言「接觸效應」來解釋「入歸柳」和「入歸語」產生的動機以及各種變體互相競爭或融合的機制。

The initial /j-/ in Southern Min roughly coresponds to the ＂ri＂ consonant in ancient Chinese. There are two main variants [j-] and [l-] of this consonant which boundary is overlapping roughly with that of the Zhangzhou and Quanzhou. After Southern Min immigrated into Taiwan, The [j-] variant predominated in Taiwan, and another [g-] variant emerged somewhere. But the result of socio-dialectological survey conducted recently shows that the [l-] has become the new trend of phonological change in Taiwan. No matter in Minnan or in Taiwan, [l-] shows strong competitive edge. This paper is aimed at clarifing the process of the split, competition and fusion of the dialectal variants of the /j-/ initial and explainning their mechanism with the effects of population, markedness, pattern congruity, Hakka substratum and language contact.