This article provides an improved method of calculating productivity index in order to calculate the productivity of each usage of polysemous or multifunctional words. The new method utilizes the standardized TTR, which strongly correlates with the index previously proposed. This case study classifies 20,000 examples of the aspect marker
-teiru into four meaning groups: continuation, result, experience, and state. The productivity of each group is then calculated, resulting in a value decrease in the same sequence. This result also matches previous studies of the acquisition of
-teiru. Furthermore, as a byproduct of this study, a list showing which meaning a verb tends to have was created. Most verbs tend to have one of four meanings.
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