Soumatome 20 Lessons JLPT N4 Grammar Lesson 20: Sentence styles: Polite, casual & contracted

The polite style is used when speaking to a superior at work or to someone you have just met or do not know well.

The polite style is used in formal contexts such as announcements and broadcasting, and is also common in writing. Plain style may, however, be used in letters to people close to you.

The plain style is used when speaking with family and friends, and for notes or diaries.

The plain style is used in newspaper/news writing.

Plain style is used in reports, essays, and academic prose, often with だ／である according to the required style. In hierarchical conversation, a senior may use plain style while a junior uses polite style, but this is not automatic: familiarity, organizational culture, and the situation govern the choice, and misplaced plain speech may sound curt.

When speaking with people close to you, shortened expressions called contracted forms are common.
Vてしまう → Vちゃう; Vでしまう → Vじゃう; Vている／Vていた → Vてる／Vてた; Vておく → Vとく; Vてはだめ → Vちゃだめ; Nではない → Nじゃない; Vのだ → Vんだ; Vなければ → Vなきゃ; V(plain)と言った → V(plain)って言った.

Vocabulary must match context and style. These are approximate choices, not mechanically interchangeable pairs: しかし／だが ↔ だけど／けど; (行った)が／けれども ↔ (行った)けど; たいへん／非常に ↔ すごく／とっても; あまり ↔ あんまり; こちら／そちら／あちら／どちら ↔ こっち／そっち／あっち／どっち. 「だって～もん」 gives a reason with a defensive or emotional tone; it is highly casual and can sound childlike, so it differs pragmatically from formal 「それは～からです」.

In casual conversation, particles such as は・が・を・か and polite endings such as ～ください・～ですか may be omitted or shortened when the listener can still recover the relationships and intent. Omission is not always possible: retain them when dropping them would create ambiguity, alter focus, or make the sentence hard to understand.