敬體→常體——一張表搞定所有變形

Japanese has two speaking styles: polite form (丁寧体) and plain form (普通体/常体).

• Polite form: Uses ます / です. Formal and polite. Used with superiors and strangers.
• Plain form: No ます / です. Short and casual. Used with friends and family.

Starting from N4, textbooks heavily use plain form. If you only know polite form, you won't be able to connect with later grammar — because nearly all grammatical patterns require plain form before them.

Why Learn Plain Form?

You already know the polite forms:

飲みます / 飲みません / 飲みました / 飲みませんでした

When Japanese people talk with friends, they don't say it that way — it's too long. They say:

飲む / 飲まない / 飲んだ / 飲まなかった

Much shorter, right? That's the plain form. Moreover, almost all grammar patterns you'll learn from N4 onward (ので, のに, と思う, ～とき...) require plain form. So this conversion chart is the foundation for everything that follows.

Verb Plain Form

The plain form of a verb is simply its dictionary form — you've already seen it:

Conversion rules:

• Affirmative present: ます → dictionary form (飲みます → 飲む)
• Negative present: ません → ない (飲みません → 飲まない)
• Affirmative past: ました → た (飲みました → 飲んだ)
• Negative past: ませんでした → なかった (飲みませんでした → 飲まなかった)

Let's verify with an ichidan verb:

Key point: The ない in verb negation and the ない in adjective negation look the same but are fundamentally different. The verb's ない is an auxiliary verb, while the adjective's ない is part of the adjective ending. Just keep this distinction in mind for now.

I-Adjective Plain Form

The i-adjective conversion is the simplest — just remove です:

Note: The negative polite form actually has two variations — 高くないです and 高くありません — both mean the same thing. The plain form for both is 高くない.

Na-Adjective Plain Form

Na-adjectives use だ to replace です:

Conversion rules:

• です → だ
• ではありません → ではない
• でした → だった
• ではありませんでした → ではなかった

Noun Sentence Plain Form

Good news — noun sentences follow the exact same pattern as na-adjectives:

Remember this: Nouns and na-adjectives follow identical conjugation rules. Learn one set and you've got both.

Where Does だ Come From?

You might wonder: why is the plain form だ and not something else?

The ancestor of です is actually である (written/formal style):

So だ / です / である are essentially the same word, just at different levels of formality.

Complete Conversion Chart

Summary

• Verbs: Plain form = dictionary form; negative uses ない, past uses た, past negative uses なかった
• I-adjectives: Just remove です
• Na-adjectives / Nouns: です → だ, ではありません → ではない, and so on
• Nouns and na-adjectives follow the exact same pattern — learn one, get both
• だ / です / である are the same thing at different formality levels

Practice

Q1. Convert 食べません to plain form.

Q2. What is the polite form of 静かだった?

Q3. Which one is plain form? A. 高くないです　B. 高くない