Linguistic difference often, if not always, reflects, maintains or reinforces inequality between social groups, as is shown in the present author's previous paper. The present paper attempts to clarify the process through which linguistic difference performs such functions. The linguistic difference between social group is actually a quantitative one not to be reduced to the bipolar or binary category of total difference or total identity. An examnination of historical and contemporary examples clearly shows that actual linguistic difference is realized as a bundle of quantitative differences of individual linguistic items, and caused by a variety of factors including the difference between the groups in question. In perception, however, the difference is reduced to the bipolar form of simple difference or identity, and ascribed to a single factor, that is, the group difference. More importantly, such perception is frequently accompanied by a binary value judgment on the groups concerned. Thus, the actual quatitative multi-faceted linguistic difference not to be attributed to a single factor is transferred to the binary value judgment about the social groups in question, whihc perfoms functions of reflecting, maintaining, reinforcing, or, in some cases, revolting against, the existing unequal relationship.