First Published in 2002. This volume is part of the 'Outstanding Dissertations in Linguistics' series. This study focuses on the Japanese particle mo. The particle is probably best described as roughly equivalent to the English too or also, although the difference between the Japanese particle and the English counterparts will be soon revealed as an important part of this study. This study has two goals, which are related to one another. The first goal is to prescribe a monosemous account for what is presupposed by the usage of mo by investigating its constraints on the context. The second goal is to develop a model in which the discourse-level contribution of a linguistic form is explained by its instruction on the hearer's processing the sentence at the propositional level.