When to use plain and polite Japanese forms

Distinguish a grammatical form from overall style

Plain forms include non-past, negative, past, and past negative, not only the dictionary form. Polite forms commonly use the です/ます system to address the listener politely. Plain or polite style describes the prevailing sentence endings in speech or writing. A polite sentence may still require plain forms within it.

For 読む, the four plain forms are 読む, 読まない, 読んだ, and 読まなかった. Their polite counterparts are 読みます, 読みません, 読みました, and 読みませんでした. 読みました is polite past, not plain past; removing ました does not produce 読みた. Check the verb’s group and conjugation before selecting style.

Conjugate verbs, i-adjectives, na-adjectives, and nouns separately

Not every predicate can simply take ます or だ. The i-adjective 高い has no だ in its plain ending; polite non-past is 高いです and polite past is 高かったです. Nouns and na-adjectives often end in だ or だった in plain statements and です or でした in polite ones.

Polite negatives have natural alternatives, including 高くないです/高くありません and 学生ではないです/学生ではありません. Practice a consistent basic set before recognizing conversational じゃ variants. A longer expression is not automatically the best choice for every situation.

• Verb: 食べる / 食べない / 食べた / 食べなかった; polite 食べます / 食べません / 食べました / 食べませんでした.
• I-adjective: 高い / 高くない / 高かった / 高くなかった; polite 高いです / 高くないです / 高かったです / 高くなかったです.
• Na-adjective: 静かだ / 静かではない / 静かだった / 静かではなかった; polite 静かです / 静かではありません / 静かでした / 静かではありませんでした.
• Noun: 学生だ / 学生ではない / 学生だった / 学生ではなかった; polite 学生です / 学生ではありません / 学生でした / 学生ではありませんでした.

Plain forms can occur inside polite sentences

In 「昨日買った本を読みます。」 (I will read the book I bought yesterday), 買った modifies 本 while 読みます keeps the ending polite. In 「明日は晴れると思います。」 (I think it will clear up tomorrow), 晴れる is plain and 思います is polite. Do not make 買いました本 or 晴れますと思います merely to make the entire sentence sound polite.

Learn each connection: nouns and na-adjectives take だ before と思います, as in 「便利だと思います。」, but noun modification uses 「便利な道具」, not 便利だ道具. Direct quotation can retain the speaker’s polite wording: 「『明日行きます』と言いました。」 (They said, “I will go tomorrow.”) This differs from the plain-form-plus-と思います practice; not every quotation requires removing ます.

Choose endings by relationship and situation

With a new acquaintance, someone you do not know well, or a generally formal service interaction, です/ます is a useful starting point. Close friends may use plain style, but consider preferences, relationships, and the situation. Being the same age does not automatically license a switch. Plain style is not inherently rude, and polite endings do not repair an inappropriate demand.

です/ます primarily expresses politeness to the listener. Respectful and humble language also concerns the actor and recipient, with forms such as いらっしゃる and 伺う in appropriate contexts. Adding ます everywhere does not cover the whole honorific system. Written style follows genre too: personal notes may be plain, while a formal report may use である. Avoid unmotivated shifts within one passage.

Mark the ending, then check embedded structures

Circle the sentence ending and bracket noun modifiers or thought content. Preserve meaning and tense when changing style; changing to plain style does not mean changing past to non-past. Our verified Minna Beginner Lesson 20 includes plain conversations and several predicate types for comparison with earlier polite patterns.

These original tasks check past conjugation, i-adjectives, noun modification, and opinions. Afterwards write one statement for a friend and another for a new acquaintance, explaining your ending choice and retained embedded plain forms. This is not claimed as teacher-reviewed or automatically graded material.