This paper illustrates the importance of zero pronouns as a tool in assessing the difficulty of Japanese reading materials. Zero pronouns (henceforth 'zeros') are the referential noun phrases (NPs) that are not overtly expressed in Japanese sentences. These NPs can be omitted if they are recoverable from a given context or relevant knowledge. The use of 'zeros' is common in Japanese and this poses a challenge for Japanese language learners for their accurate comprehension of Japanese sentences with 'zeros'. However, unlike Kanji or vocabulary, 'zeros' have not been considered to be an indicator to gauge the difficulty of Japanese reading materials. Therefore, in this paper, we demonstrate that 'zeros' can be further categorized according to the types of their referents. We further propose that knowing the different types of 'zeros' and their distribution in the text can help the instructor to determine the difficulty level of the text.
First, we illustrate different types of 'zeros' and propose their categorization according to the types of their referents. We introduce nine categories of 'zeros': local, semantic, global, contextual, event, indeterminate, time/weather, cataphora and first and second person pronouns. Second, based on this categorization, we examine reading materials in an intermediate-level Japanese language textbook. The results of the analysis show the frequencies and the diverse use of 'zeros' in various categories in the text. Third, interpretations of 'zeros' by 20 intermediate Japanese language learners are analyzed using the categorization proposed above. Results indicate that certain categories of 'zeros' are harder to interpret than other categories. In other words, the types of 'zeros' can be used to predict difficulty in interpreting 'zeros'. Therefore, we propose that it is reasonable to include 'zeros' as a valuable tool to assess the difficulty level of reading materials in Japanese language teaching.