Plain Form vs. Polite Form

You’ll be able to

Distinguish the polite (です／ます) style from the plain (dictionary) style
Convert between plain and polite verb forms
Choose the appropriate register for a given social situation

Two registers of Japanese

Japanese speech comes in two everyday registers. The polite form (丁寧体, teineitai) ends sentences in です and ます: 食べます (tabemasu, “eat”), 学生です (gakusei desu, “am a student”). It is the safe default with strangers, teachers, and elders. The plain form (普通体, futsūtai), also called the dictionary/casual form, ends in the bare verb or だ: 食べる (taberu, “eat”), 学生だ (gakusei da). It is used among friends, family, and in most writing. Choosing the register signals your relationship to the listener.

Converting polite to plain

The dictionary (plain) form is the base; the polite ます form is derived from it. For ru-verbs (ichidan), drop る and add ます: 食べる → 食べます (taberu → tabemasu). For u-verbs (godan), change the final -u sound to -i and add ます: 飲む → 飲みます (nomu → nomimasu), 話す → 話します (hanasu → hanashimasu). The plain negative uses ない (食べない, tabenai, “don’t eat”); the polite negative uses ません (食べません, tabemasen). Nouns and な-adjectives pair with だ (plain) or です (polite).

Reading the social situation

Register is not just grammar — it is social positioning. Use polite です／ます with people of higher status, in public or first-meeting situations, and in formal writing like essays. Use plain form with close friends, younger people, family, and in personal diaries or casual chat. Mismatching stings both ways: plain form to a teacher sounds rude, while stiff です／ます among close friends can sound cold or distant. Reading the relationship correctly is a core cultural skill.

Worked example

Take the plain-form sentence 毎日日本語を勉強する (Mainichi Nihongo o benkyō suru, “[I] study Japanese every day”) and convert it to the polite form for talking to a teacher.

1.Identify the verb: 勉強する (benkyō suru, “to study”) is an irregular する-verb.
2.The polite form of する is します (shimasu).
3.Replace する with します, keeping the object 日本語を and time word 毎日 unchanged.
4.Result: 毎日日本語を勉強します (Mainichi Nihongo o benkyō shimasu).

Answer: 毎日日本語を勉強します。(Mainichi Nihongo o benkyō shimasu.) “[I] study Japanese every day.” Only the sentence-final verb changes register — する becomes the polite します — while the particles and other words stay the same. This is the form to use with a teacher.

Checkpoint

What is the polite (ます) form of the plain verb 飲む (nomu, “to drink”)?

Watch out

Do not mix registers within one stretch of speech. If you start a conversation in polite です／ます, stay polite; suddenly dropping to plain form can read as abrupt or disrespectful. Consistency of register is itself part of sounding natural and appropriate.

Checkpoint

You are speaking with your homeroom teacher for the first time. Which sentence is most appropriate?

On the exam

On AP tasks, register is scored. The interpersonal email reply and formal speech generally call for です／ます; a casual message to a friend may use plain form. Read the prompt for cues about who the audience is, and keep your chosen register consistent to the end.

Answer the 2 checkpoints as you read.