The ない-form is the base negative form of a verb. It is used on its own in casual speech and as a building block for many grammar patterns such as 〜なくてはいけない and 〜ないでください (later). Key points: • ない-form = casual negative • Built differently for each verb group • Used before patterns like なくてはいけない • Irregular: する→しない, 来る→こない For u-verbs, change the final vowel to the a-sound and add ない: 書く→書かない, 読む→読まない, 行く→行かない. For ru-verbs, drop る and add ない: 食べる→食べない, 見る→見ない. The ない-form is essential for making obligations and prohibitions. If you learn this form, many other patterns become easy to build. At N5, focus on common verbs and memorize their ない-forms. Once you see them often, the pattern becomes natural. Remember to keep the form consistent with casual style. If you need polite speech, use ません instead.