This paper studies the meanings and functions of "ippo" in modern Japanese by investigating practical example sentences. Previous research mainly focuses on the usage of "ippo" as a conjunctive particle in a format of "ippode" connecting to a verb. However, no literature has reported on the usages of "ippo" as a pseudo noun or a postposition. In this paper, the usages of "ippo" are described in the three cases of meanings and functions: (1) pseudo noun, (2) postposition, and (3) conjunctive particle. The results of the study are presented as follows.
First, when "ippo" is used as a pseudo noun, two different meanings are considered, which are "one direction" and "one side". In both meanings, "ippo" represents a space indicated by a front noun and "N+ippo" takes several cases. In this case, "N+ippo" functions as a pseudo noun.
Second, when "ippo" is used as a postposition, it implies a different view from a point indicated by a front noun. In this case, the form of "ippo" is only limited to "N+ippode" or "N+ippo", and then "N+ippo" functions as a postposition.
Third, when "ippo" is used as a conjunctive particle, it represents a different aspect from a point indicated by a front verb. In this case, the form of "ippo" is limited to "V+ippode" or "V+ippo", and then "V+ippo" functions as a conjunctive particle.
In conclusion, "ippo" is used as a postposition or a conjunctive particle, although its basic function is a pseudo noun and it represents a space in modern Japanese. As a postposition or a conjunctive particle, "ippo" shows significant changes in both aspects of formats and meanings.