ない形

The ない form (plain negative) is a foundational part of Japanese grammar. While it is used as a standalone verb in casual conversation, it also serves as the base for many other grammar patterns.

Conjugation Rules:

• Group 1 (Godan Verbs): Change the final -u vowel to the -a vowel in the same row of the hiragana chart, then add ない.
  Example: 書く（かく）→ 書かない（かかない）.
  Special Rule: If the verb ends in a plain う, it changes to わ, not あ.
  Example: 買う（かう）→ 買わない（かわない）.
  Note: Some verbs ending in いる or える are actually Godan verbs and follow this rule, such as 帰る（かえる）→ 帰らない（かえらない）.
• Group 2 (Ichidan Verbs): Simply remove the final る and add ない.
  Example: 食べる（たべる）→ 食べない（たべない）.
• Group 3 (Irregular Verbs):
  する (to do) becomes しない.
  来る（くる, to come）becomes 来ない（こない）. Note the change in the kanji reading!
• The 「ある」 Exception: The negative of ある (to exist) is simply ない.

Polite Alternatives:
While ません is the standard polite negative, it is also very common in modern spoken Japanese to add です after the plain negative form (e.g., 食べないです) to create a polite negative sentence.

Usage and Extensions:
This form is used for casual negation ('I don't eat') and future intent ('I won't go'). It is also the essential base for several key structures:

• Casual Invitations: When used as a standalone verb with rising intonation, the ない form is heavily used for casual invitations or suggestions. For example, 一緒に行かない？（いっしょにいかない？）means 'Want to go together?'.
• Noun Modification: Unlike polite forms, the plain negative can directly modify nouns (e.g., 食べない人 - a person who doesn't eat). This is a primary reason for learning the plain form.
• Obligation: Combined with other particles to form なければならない (must). In casual speech, this is often contracted to なきゃ or なくちゃ.
• Requests: Used in ないでください (please don't).
• Connecting Sentences: When connecting negative clauses, use ないで to mean 'without doing' or なくて to express a reason or a simple 'and not' contrast.
• Conditionals: By dropping the い and adding ければ or かったら, you create the negative conditional ('if you don't [verb]'). For example, 食べなければ or 食べなかったら (if you don't eat).

Once a verb is in the ない form, the ない ending behaves exactly like an い-adjective. This means to make it past tense, you change it to なかった. Just as you can add です to the present tense, you can add it to the past tense to make なかったです, which is the modern spoken equivalent to ませんでした.