This thesis studies the Japanese verbal suffix -aw that is used in sentences that express the concept of reciprocity. Some languages like English employ a nominal reciprocal such as each other to express reciprocity, while other languages like Japanese use a verbal reciprocal like -aw. The semantic property of the verbal reciprocal has not received as much attention as that of the nominal reciprocal in modern linguistics. This thesis proposes a detailed analysis of the Japanese verbal reciprocal and contributes to the understanding of how reciprocity is expressed in natural languages. The study of reciprocity involves many important aspects of semantic research, such as plurality, quantification, and compositionality. Thus, the outcome of this thesis is expected to provide further knowledge of these aspects based on a lot of undiscussed data of the Japanese verbal reciprocal.

The Japanese verbal reciprocal is used not only in reciprocal sentences, but also in non-reciprocal sentences that do not seem to express reciprocity in the traditional sense. I argue that such non-reciprocal sentences involve a reciprocal component and propose a denotation of the non-reciprocal use of -aw that compositionally yields the non-reciprocal interpretations. A minimally extended denotation is proposed for the canonical reciprocal use of -aw. I demonstrate the compositional semantic analysis of the reciprocal sentences to show that the proposal makes correct predictions for the interactions with other verbal morphologies.

The discussion of the Japanese verbal reciprocal continues to the crosslinguistically observed phenomenon of the so-called discontinuous reciprocal. The verbal reciprocals in many languages including Japanese allow a singular subject and an oblique or a comitative phrase to form an apparently discontinuous plural argument. I propose that the Japanese verbal reciprocal employs this mechanism of a discontinuous plural argument that is independently available for plural predication.

The detailed investigation of the Japanese verbal reciprocal suggests a typological diversity of the apparently uniform phenomena. The non-reciprocal use of a verbal reciprocal is often observed in other languages, but a comparison of data from Japanese and other languages such as Madurese and Cusco Quechua seems to call for a non-uniform treatment. In addition, the discontinuous reciprocal found in languages like Hebrew and Greek seems to be fundamentally different from that in Japanese, Malagasy, and Bantu languages. This consequence of the current inquiry of the Japanese verbal reciprocal forms a foundation for future research about verbal reciprocals in natural languages.