Abstract
The aim of this paper is to propose a new way of quantifying the productivity of 103 functional words taught in a Basic Japanese Course. To measure productivity beyond large differences between token-frequency of items, seven candidate measures are prepared. Then, 103 items in BCCWJ are calculated for every 7 indexes. After that, the candidates were evaluated from several perspectives. As a result, the formula equivalent to Guiraud Index is the most suitable: Type divided by square root of Token. And the results are consistent with the preceding insights regarding the descriptive grammar of Japanese. High-productive items mainly correspond to time; since they involve no constraint on verb meanings, they can collocate with any verbs. Low-productive items, in contrast, contain a lot of markers for asking, proposal, and prohibition, as well as honorifics. These all are used more in oral communication than in written words. Finally it is claimed that this new index can contribute to education of Japanese language, because we can know which items can co-occur with many verbs or situation and which not, which is necessary information for Japanese Language Education.
https://ror.org/03zhhr656 
