Tense in Japanese grammar is a slightly different concept compared to English grammar. In English, tense refers to the time at which an action takes place, such as the past, present, or future. In Japanese, however, tense is not expressed in the same way. Instead, the focus is on the aspect of the action, whether it is in progress, completed, or habitual.

There are two main tenses in Japanese: past and non-past. The past tense indicates that an action has already occurred, while the non-past tense includes both present and future actions. Within each tense, there are various verb forms to express different aspects of the action.

For example, the past tense can be expressed using the plain past form, the polite past form, or the te-form plus shimau, depending on the level of formality and the nuance you want to convey. Similarly, the non-past tense can be expressed using the plain non-past form, the polite non-past form, or the te-form, among others.

Understanding tenses in Japanese requires not only knowing the verb forms but also paying attention to the context and the specific particles used in the sentence.