Familiar category terms, such as ‘noun’, ‘verb’, and ‘adjective’, are usually used in language classes. However, the application of these labels in the target language is not necessarily intuitive. English learners of Japanese often have problems with: (i) ‘deverbal nouns’, problems that stem from the ‘noun–verb’ distinction, and (ii) ‘adjectives’, which are divided into two types unlike English ‘adjectives’. This article builds on these examples toward an analysis of Japanese involving four categories defined by the intersection of the nominative case and tense markers. The moral is that a language could be learned more accurately and readily if categories were based on such salient distinctions in the target language.