じゃないIs not, Isn't

The negative form of a る-verb indicates 'does not' or 'will not' do something (e.g., 食べない = 'I don't eat' or 'I won't eat'). In contrast, じゃない (a casual form of ではない, the negative of だ) negates nouns and な-adjectives (e.g., 元気じゃない = 'not feeling good'). While both express negation, they apply to different types of words.

だ follows nouns and な-adjectives, with a meaning similar to the English 'is.' For instance, これはペンだ translates to 'This is a pen.' On the other hand, じゃない (a contraction of ではない) is used to create the negative of such expressions. For example, これはペンじゃない translates to 'This isn't a pen.'

です works like 'is' or 'to be' in English and is used to politely state something in everyday conversation. じゃない is the casual negative form meaning 'is not,' and it's often used in relaxed speech or in phrases like ～じゃないと思います ('I don't think it is...').

じゃない follows a noun or な-Adjective to express 'is not' or 'are not.' じゃないか, with the addition of か, changes the meaning to 'Isn't it...?' as in 本じゃない ('It isn't a book') vs. 本じゃないか ('It's a book, isn't it?') While じゃない is used only after nouns or な-Adjectives, じゃないか can follow い-Adjectives and verbs as well.

じゃない and じゃなかった both follow nouns or な-adjectives to express the negative, but differ in tense. じゃない is present tense ('is not'), while じゃなかった is past tense ('was not'). For example, 静かじゃない means 'It isn't quiet,' while 静かじゃなかった means 'It wasn't quiet.'

い-Adjectives form a negative by replacing い with くない (e.g., 赤い = 'it's red,' 赤くない = 'it's not red'). For nouns and な-Adjectives, the negative is formed by adding じゃない (e.g., 大変じゃない = 'it's not difficult,' バナナじゃない = 'it's not a banana'). Both forms are plain and used in casual conversation or other grammatical patterns.

The negative form of an う-verb indicates 'does not' or 'will not' perform an action (e.g., 買わない = 'I don't buy' or 'I won't buy'). On the other hand, じゃない (casual form of ではない, the negative of だ) negates nouns and な-adjectives (e.g., 元気じゃない = 'not feeling good'). Both express negation, but each applies to different word types.