In Japanese, adjectives and nouns can also be used in plain and polite forms to describe people, objects, and situations. Understanding these forms is essential for making natural sentences in conversation and writing.

1. Adjectives

Japanese adjectives are mainly divided into i-adjectives (い-adjectives) and na-adjectives (な-adjectives).

a) I-Adjectives (い-adjectives)

Plain Form Present: Keep the adjective as it is. Example: たかい (takai → high/expensive) → たかい (takai → is high/expensive)

Polite Form Present: Add です. Example: たかい → たかいです (takai desu → is high/expensive)

Plain Form Past: Replace い with かった. Example: たかい → たかかった (takakatta → was high/expensive)

Polite Form Past: Replace い with かったです. Example: たかい → たかかったです (takakatta desu → was high/expensive)

Negative Forms:

Plain: たかくない (takakunai → not high/expensive)

Polite: たかくないです / たかくありません (takakunai desu / takaku arimasen → not high/expensive)

Past Negative: たかくなかった (takakunakatta → was not high), たかくなかったです (takakunakatta desu → was not high)

Examples:

このビルはたかいです。→ This building is tall.

このくつはたかかったです。→ These shoes were expensive.

このえんぴつはたかくないです。→ This pencil is not expensive.

b) Na-Adjectives (な-adjectives)

Plain Form Present: Add だ after the adjective. Example: しずか (shizuka → quiet) → しずかだ (shizuka da → is quiet)

Polite Form Present: Add です. Example: しずか → しずかです (shizuka desu → is quiet)

Plain Form Past: Add だった. Example: しずか → しずかだった (shizuka datta → was quiet)

Polite Form Past: Add でした. Example: しずか → しずかでした (shizuka deshita → was quiet)

Negative Forms:

Plain: しずかじゃない (shizuka janai → not quiet)

Polite: しずかじゃないです / しずかではありません (shizuka janai desu / shizuka dewa arimasen → not quiet)

Past Negative: しずかじゃなかった (shizuka janakatta → was not quiet), しずかじゃなかったです (shizuka janakatta desu → was not quiet)

Examples:

このへやはしずかです。→ This room is quiet.

きのうのへやはしずかでした。→ Yesterday’s room was quiet.

このへやはしずかじゃなかったです。→ This room was not quiet.

2. Nouns

Japanese nouns use copula verbs to express existence or description. The main copula verbs are だ (plain) and です (polite).

Plain Form Present: Noun + だ

せんせいだ → is a teacher

Polite Form Present: Noun + です

せんせいです → is a teacher

Plain Form Past: Noun + だった

せんせいだった → was a teacher

Polite Form Past: Noun + でした

せんせいでした → was a teacher

Negative Forms:

Plain Present: せんせいじゃない → is not a teacher

Polite Present: せんせいじゃないです / せんせいではありません → is not a teacher

Plain Past: せんせいじゃなかった → was not a teacher

Polite Past: せんせいじゃなかったです / せんせいではありませんでした → was not a teacher

Examples:

かれはせんせいです。→ He is a teacher.

かのじょはがくせいだった。→ She was a student.

かれはせんせいじゃなかったです。→ He was not a teacher.

Tips and Tricks:

1. Remember i-adjectives change the い ending for past and negative forms, while na-adjectives use だ / です with minor adjustments.

2. Use です for polite speech in both adjectives and nouns.

3. Practice combining nouns and adjectives with plain and polite past to tell stories or describe experiences.

4. For casual conversation, plain form is enough; for formal writing or talking to teachers, polite form is better.

5. Use negative forms naturally: 〜くない for i-adjectives, 〜じゃない for na-adjectives and nouns.

Mastering adjectives and nouns with plain and polite forms allows Japanese learners to describe things accurately, talk about the past, and make polite or casual statements in conversations. Practice regularly with examples to make using these forms natural.

Japanese Adjectives and Nouns – Plain and Polite Forms Explained