Section 1: The Plain Form in Use

Plain-form Japanese is not a register you shift into — it is the baseline grammar of the language. Polite forms (〜ます, 〜です) are additions to that base, layered on for social distance. When those layers come off in casual speech, what remains is not broken or simplified Japanese. It is structurally complete Japanese, and it is what native speakers use with friends, family, and anyone inside their social circle. Textbooks teach plain forms as grammar building blocks — something you conjugate through on the way to the polite form — but rarely present them as the default surface of actual conversation. This section establishes what plain-form predication sounds like in practice: how statements, negations, questions, requests, and conjectures all work without the polite scaffolding. Every pattern in the rest of this book assumes you are comfortable with what is covered here. If the entries in this section feel obvious when you read them in isolation, that is expected. The difficulty is hearing them at native speed, stacked together, with particles dropped and intonation doing the work that ます and か used to do.

1.1 だ（述語）

← 教科書の形: 〜です

Formula: [N] / [na-adj] + です → [N] / [na-adj] + だ

Register: ★★★ core Medium: spoken — all

Gap Note

Genki I introduces だ as the plain equivalent of です in its grammar notes but almost never uses it in example conversations, which remain in polite form throughout. Minna no Nihongo similarly keeps だ confined to subordinate clauses (〜だと思う, 〜だから). The result is that learners understand だ as a conjugation exercise but have no feel for it as a live sentence-ender. When they hear someone end a sentence with 大丈夫だ instead of 大丈夫です, it can sound blunt or even aggressive — when in reality it is simply neutral casual speech between peers.

How the transformation works

Replace です at the end of a noun or な-adjective predicate with だ. With い-adjectives and verbs in plain form, だ does not appear — those predicates are already complete without a copula (see 1.2).

Examples

[casual / college student describing a friend's new apartment] ここ、駅から近くて便利だ。 This place is close to the station — it's convenient.

[casual / two friends at a restaurant, looking at the menu] これ、結構高いな。でもこっちは普通だ。 This one's pretty expensive. But this one's normal.

[casual / coworker commenting on an assignment at a small company] あの仕事、来週までだ。 That job's due by next week.

[casual / friend reacting to news, with sentence-final particle (→ 4.2)] え、マジだよ。昨日聞いた。 Seriously, it's for real. I heard yesterday.

[casual / older brother to younger sibling] まだ無理だ。もうちょっと待て。 It's still no good. Wait a bit longer.

[polite equivalent for comparison] まだ無理です。もう少し待ってください。 It's still not possible. Please wait a little longer.

Dialogue

[casual / two university friends, A male, B female, discussing weekend plans]

A: 土曜、暇？　[You free Saturday?]

B: 午前は用事だけど、午後は暇だよ。　[I have stuff in the morning, but I'm free in the afternoon.]

A: じゃあ映画行かない？新しいの、結構よさそう。　[Then wanna go to a movie? The new one looks pretty good.]

B: いいね。何時にする？　[Sounds good. What time?]

A: ２時ぐらいでどう？　[How about around two?]

B: オッケー、２時だね。　[Okay, two it is.]

Contrast with

1.2: ∅（い形容詞文末） — い-adjectives do not take だ; adding it is a common learner error

1.2 ∅（い形容詞文末）

← 教科書の形: 〜いです

Formula: [i-adj] + です → [i-adj] + ∅

Register: ★★★ core Medium: spoken — all

Gap Note

Genki I teaches 〜いです as the polite form of い-adjective predicates and notes that the plain form is simply the adjective alone. But because drills and model dialogues overwhelmingly use the polite form, learners internalize 〜いです as the "real" sentence and the bare adjective as something grammatically incomplete. Hearing 暑い as a full, finished utterance — without です, without a particle — feels like something is missing. It is not. The adjective alone is a complete predicate.

How the transformation works

Remove です. The い-adjective in dictionary form is already a complete predicate in Japanese and requires no copula. Do not add だ — い-adjective + だ is ungrammatical in standard speech.

Examples

[casual / stepping outside on a summer day, speaking to a friend] うわ、暑い。 Ugh, it's hot.

[casual / tasting food a friend cooked] これめっちゃおいしい。 This is super good.

[casual / scrolling through an online store with a friend] 高い。他のにしよう。 It's expensive. Let's go with a different one.

[casual / watching a movie trailer, with sentence-final particle (→ 4.1)] 面白そうだね。でも長いな。 Looks interesting. But it's long.

[casual / friend commenting after a hike] 足痛い。もう歩きたくない。 My feet hurt. I don't wanna walk anymore.

Dialogue

[casual / two coworkers on lunch break, A female, B male]

A: 今日の弁当、量多くない？　[Isn't today's bento kind of a lot?]

B: 朝から何も食べてないから、ちょうどいい。　[I haven't eaten anything since this morning, so it's just right.]

A: えー、それ体に悪いよ。　[Ew, that's bad for you.]

B: 分かってるけど、朝は眠い。無理。　[I know, but mornings are sleepy. Can't do it.]

Contrast with

1.3: ∅（述語省略） — zero copula with な-adjectives and nouns is a different phenomenon

1.3 ∅（述語省略）

← 教科書の形: 〜です / 〜だ

Formula: [N] / [na-adj] + だ → [N] / [na-adj] + ∅

Register: ★★★ core Medium: spoken — all

Gap Note

Textbooks present だ as the plain copula and stop there. Neither Genki nor Minna no Nihongo mentions that in actual casual speech, だ itself frequently drops — especially in female speech and in utterances that end with a particle (ね, よ, かな). A learner who has just gotten comfortable with だ as the casual copula now encounters sentences like うん、元気 or 明日、休みよ and wonders where the verb went. There is no verb. The predicate is simply the noun or な-adjective, standing alone.

How the transformation works

Drop だ entirely. The noun or な-adjective sits at the end of the sentence with nothing after it, or is followed directly by a sentence-final particle. This is especially common before よ, ね, and in questions with rising intonation (→ 1.9). Retaining だ before certain particles (だよ, だね) is also grammatical and common — the zero-copula form is an alternative, not a replacement.

Examples

[casual / answering the phone, friend asks how you are] うん、元気。そっちは？ Yeah, I'm fine. How about you?

[casual / texting a friend about tomorrow's plan] 明日、休み。 Tomorrow's a day off.

[casual / female speaker commenting on a mutual friend's outfit, with particle (→ 4.2)] あの服、すごくきれいよ。 That outfit is really pretty.

[casual / friends deciding where to eat] あそこ、静かだし、料理もおいしいし。 That place is quiet, and the food's good too.

[casual / responding to a question about one's major] 経済。あんまり面白くないけど。 Economics. Not that interesting, though.

Dialogue

[casual / couple deciding what to eat for dinner, A female, B male]

A: 今日、何にする？　[What should we do for today?]

B: カレーでいいんじゃない？　[Curry's fine, isn't it?]

A: えー、昨日もカレーだったじゃん。　[Ugh, it was curry yesterday too.]

B: じゃあパスタ？　[Then pasta?]

A: パスタ、いいね。　[Pasta — sounds good.]

Variations

∅ + 粒子（ゼロ述語＋助詞） Formula: [N] / [na-adj] + ∅ + (ね / よ / かな)

[casual / looking at rain outside] 今日、雨かな。 I wonder if it'll rain today.

Contrast with

1.2: ∅（い形容詞文末） — い-adjectives never had だ to begin with; this entry is about nouns and な-adjectives losing their copula

1.4 〜ない

← 教科書の形: 〜ません

Formula: [V-masu stem] + ません → [V-nai]

Register: ★★★ core Medium: spoken — all

Gap Note

Genki I teaches the 〜ない form early as a conjugation pattern, and learners can produce it on worksheets without trouble. But Genki's dialogues almost exclusively use 〜ません in conversation, so learners rarely see 〜ない functioning as a live sentence-ender between speakers. Minna no Nihongo follows the same pattern. The consequence is that when a drama character says 知らない as a complete reply, the learner may parse the grammar correctly but misjudge the tone — hearing it as rude or aggressive when it is simply the default casual negative. The bluntness is relative to 〜ません, not absolute.

How the transformation works

Use the plain negative form of the verb (〜ない) as the sentence-final predicate, without です or any polite suffix. For い-adjectives, the negative is already 〜くない. For だ predicates, the negative is じゃない (→ 5.10). The 〜ない form is structurally an い-adjective and conjugates like one (〜なかった, 〜なくて).

Examples

[casual / friend asks if you saw the news] ごめん、まだ見てない。 Sorry, I haven't seen it yet.

[casual / declining an invitation] 明日はちょっと行けない。 I can't go tomorrow.

[casual / responding to a question about a mutual acquaintance] あの人のこと、全然知らない。 I don't know that person at all.

[casual / complaining about the weather, combined with trailing けど (→ 7.1)] 傘持ってないんだけど。 I don't have an umbrella, though... (implicit: what do we do?)

[casual / friend suggesting a restaurant] あそこ、あんまりおいしくないよ。 That place isn't very good.

[polite equivalent for comparison] あそこはあまりおいしくないですよ。 That place isn't very good.

Dialogue

[casual / two friends walking to a restaurant, A female, B female]

A: あ、財布忘れた。　[Oh, I forgot my wallet.]

B: え、お金ないの？　[Wait, you don't have money?]

A: カードはあるから大丈夫だと思うけど。　[I have my card so I think it's fine, but...]

B: 現金しか使えない店だったらどうする？　[What if it's a cash-only place?]

A: そしたら貸して。あとで返す。　[Then lend me some. I'll pay you back later.]

Contrast with

1.7: 〜て / 〜てよ / 〜てくれ — negative requests (〜ないで) are a separate pattern

1.5 〜た

← 教科書の形: 〜ました

Formula: [V-masu stem] + ました → [V-ta]

Register: ★★★ core Medium: spoken — all

Gap Note

Like 〜ない, the 〜た form is taught early in both Genki and Minna no Nihongo as a conjugation rule, but dialogues rarely deploy it as a sentence-ender in conversation. Learners can produce 食べた on a test but may not immediately register it as a natural, complete response when a friend says 食べた？ and they need to process both the question and the answer at conversational speed. The additional wrinkle is that 〜た serves not only as past tense but also as a marker of completion, discovery, and recollection — functions that 〜ました obscures by feeling uniformly "past tense."

How the transformation works

Use the plain past form of the verb (〜た / 〜だ) as the sentence-final predicate. No です or ます scaffolding. For い-adjectives: 〜かった. For だ predicates: だった. The form is identical to what learners already use inside subordinate clauses (〜た時, 〜たことがある) — the only change is that it now stands alone at the end of the sentence.

Examples

[casual / friend asking about lunch] うん、もう食べた。 Yeah, I already ate.

[casual / discovering a new shop while walking with a friend] あ、こんなところに店できた。 Oh, a shop opened up in a place like this.

[casual / recalling something, talking to a roommate] あ、そうだ。明日ガス屋来るんだった。 Oh, right. The gas company guy is coming tomorrow — I just remembered.

[casual / texting a friend after arriving, with rising intonation question (→ 1.9)] 着いた。もう出た？ I'm here. Have you left yet?

[casual / reacting to a friend's story] それ、前にも聞いた気がする。 I feel like I've heard that before.

Dialogue

[casual / two friends after an exam, A male, B male]

A: どうだった？　[How was it?]

B: やばかった。全然できなかった。　[It was bad. I couldn't do it at all.]

A: マジで？俺もちょっと微妙《びみょう》だったけど、まあいけたかな。　[Seriously? Mine was kinda iffy too, but I think I managed.]

B: お前、毎回そう言って受かるじゃん。　[You say that every time and then you pass.]

Contrast with

1.4: 〜ない — the plain negative; 〜なかった is the plain negative past

1.6 〜よう / 〜ようか

← 教科書の形: 〜ましょう / 〜ましょうか

Formula: [V-masu stem] + ましょう → [V-volitional]（〜よう / 〜おう）

Register: ★★★ core Medium: spoken — all

Gap Note

Genki I introduces 〜ましょう for suggestions and invitations but keeps the volitional form (〜よう / 〜おう) largely confined to the grammar note about "let's" and the volitional + と思う construction. Learners practice 行きましょう but rarely encounter 行こう as a live, sentence-final suggestion between friends. The plain volitional also carries a wider range of nuance than 〜ましょう: it can be a personal resolution (やろう — "I'll do it"), a casual invitation (行こうか — "shall we go?"), or a rallying call (始めよう — "let's begin"). Hearing it as only "let's" leads to misreading speaker intent.

How the transformation works

Replace the ます-stem + ましょう with the volitional form: for Group 1 verbs, the final う-column sound shifts to the おう-column (行く → 行こう); for Group 2 verbs, replace る with よう (食べる → 食べよう); する → しよう; 来る → 来よう. Adding か softens the suggestion into a question: 行こうか — "shall we go?"

Examples

[casual / friend at a cafe, deciding to leave] そろそろ行こう。 Let's get going.

[casual / personal resolution, talking to oneself] よし、明日から早起きしよう。 Right, I'll start getting up early from tomorrow.

[casual / inviting a friend to eat, with か for softer invitation] お腹すいたね。何か食べようか。 I'm hungry, huh. Shall we eat something?

[casual / two friends at a festival, combined with rising intonation (→ 1.9)] あっち見に行こうか？ Wanna go check out over there?

[casual / rallying friends for a group project] じゃあ始めよう。時間ないし。 Alright, let's start. We don't have much time.

Dialogue

[casual / couple on a day out, A female, B male]

A: 疲れた。ちょっと休もうか。　[I'm tired. Shall we take a break?]

B: うん。あそこのベンチ空いてるよ。　[Yeah. That bench over there is open.]

A: 飲み物買ってこようか？　[Should I go buy drinks?]

B: いいの？じゃあお茶がいい。　[You sure? Then tea, please.]

A: 了解《りょうかい》。すぐ戻る。　[Got it. Be right back.]

Variations

〜ようよ（encouraging volitional） Formula: [V-volitional] + よ

[casual / encouraging a reluctant friend] 大丈夫、一緒に行こうよ。 It's fine, let's go together.

Contrast with

1.7: 〜て / 〜てよ / 〜てくれ — requests directed at the listener; volitional includes the speaker

1.7 〜て / 〜てよ / 〜てくれ

← 教科書の形: 〜てください

Formula: [V-te] + ください → [V-te]（+ ∅ / よ / くれ）

Register: ★★★ core; くれ has masculine tendency Medium: spoken — all

Gap Note

Genki I teaches 〜てください as the standard request form and does not introduce the bare 〜て request until much later, if at all. Minna no Nihongo similarly treats 〜てください as the default. This creates a gap where learners hear 見て or 待って as requests and understand them, but cannot place them on any spectrum of politeness or directness. In particular, learners often do not realize that bare 〜て is the neutral casual request — not rude — while 〜てくれ adds assertive force and 〜てよ sits between the two, adding mild insistence. Without this spectrum, every non-ください request sounds equally blunt.

How the transformation works

Drop ください from the て-form request. The bare て-form alone is a complete, neutral casual request. Adding よ makes it mildly insistent or emphatic — the speaker wants the listener to notice the request. Adding くれ (from くれる — "to give to me") makes the request more direct and assertive; it is common in male speech and in situations where the speaker feels entitled to make the request. The spectrum runs: て (softest) → てよ (mild push) → てくれ (blunt) → てくれよ (strong insistence).

Examples

[casual / asking a friend to pass something at the table] それ取って。 Pass me that.

[casual / friend is about to leave, speaker wants them to wait] ちょっと待って。 Hang on a sec.

[casual / mild insistence, friend isn't listening] ねえ、聞いてよ。 Hey, listen.

[casual / male speaker to a close male friend, blunter request] 早くしてくれ。遅刻《ちこく》するぞ。 Hurry up. We're gonna be late.

[casual / female speaker to a sibling, emphatic] もう、静かにしてよ。 Come on, be quiet.

[polite equivalent for comparison] 静かにしてください。 Please be quiet.

Dialogue

[casual / roommates, A male, B male, A is studying]

A: なあ、ちょっとテレビ消してくれ。　[Hey, turn off the TV for me.]

B: え、今いいとこなのに。　[What, it's at the good part though.]

A: 明日テストなんだよ。頼むから静かにして。　[I have a test tomorrow. Please just be quiet.]

B: 分かった分かった。イヤホンする。　[Okay okay. I'll use earphones.]

Variations

〜ないで（negative request） Formula: [V-nai] + で

[casual / asking a friend not to tell anyone] 誰にも言わないで。 Don't tell anyone.

〜てくれない？（softened request as question） Formula: [V-te] + くれない？

[casual / politely asking a favor from a friend] ちょっと手伝ってくれない？ Could you help me out a bit?

Contrast with

1.6: 〜よう / 〜ようか — invitations that include the speaker; requests are directed at the listener

1.8 〜だろう / 〜だろ

← 教科書の形: 〜でしょう

Formula: [S (plain)] + でしょう → [S (plain)] + だろう / だろ

Register: ★★★ core; だろ has masculine tendency Medium: spoken — all

Gap Note

Genki II introduces 〜でしょう as a conjecture form ("it will probably...") and sometimes as a confirmation-seeking tag ("...right?"). The plain equivalent だろう is mentioned in passing, and the further-truncated だろ barely appears. In practice, だろう and だろ carry a wider range than でしょう: だろう can express genuine conjecture ("it'll probably rain"), while だろ — especially with rising intonation — is often a challenge or assertion seeking agreement ("I told you so, right?"). Learners who map だろ to "probably" will misread exchanges where it functions as "come on, you know that."

How the transformation works

Replace でしょう with だろう for conjecture, or だろ for the shortened, more assertive form. After い-adjectives and verbs in plain form, だろう attaches directly (行くだろう, 高いだろう). After nouns and な-adjectives, the copula だ is replaced by だろう (学生だろう, 静かだろう). The shortened だろ is almost exclusively spoken and frequently carries a tone of "you should know this" rather than neutral conjecture.

Examples

[casual / looking at the sky, genuine conjecture] 明日は雨だろう。 It'll probably rain tomorrow.

[casual / discussing a friend's exam results] あいつなら受かるだろう。 If it's him, he'll probably pass.

[casual / male speaker, assertive confirmation-seeking] だから言っただろ。 See, I told you.

[casual / combined with trailing よ (→ 4.2)] 大丈夫だろうよ。心配しすぎ。 It'll be fine. You're worrying too much.

[casual / pushing back, だろ as challenge with rising intonation] そんなの分かるだろ？ You can figure that out, can't you?

Dialogue

[casual / two friends discussing whether a mutual friend will come to a party, A female, B male]

A: 健《けん》、来るかな。　[Think Ken'll come?]

B: 来るだろ。あいつパーティー好きじゃん。　[He'll come. That guy loves parties.]

A: でも最近忙しいって言ってたよ。　[But he said he's been busy lately.]

B: まあ、声かけてみよう。来なかったら来なかったで。　[Well, let's try inviting him. If he doesn't come, he doesn't come.]

Contrast with

6.1: 〜かもしれない / 〜かも — lower certainty than だろう; かも = "might," だろう = "probably"

1.9 〜？（上昇調）

← 教科書の形: 〜ですか / 〜ますか

Formula: [S (polite)] + か → [S (plain)] + ？（↑）

Register: ★★★ core Medium: spoken — all

Gap Note

Genki I teaches か as the question marker from lesson one, and learners internalize it as essential to forming questions. What no major textbook states directly is that か on a plain-form sentence sounds interrogative in a confrontational way — 何するか？ sounds like a demand, not a friendly question. In casual speech, questions are formed by intonation alone: the sentence ends on a rise, and か disappears entirely. This is perhaps the single largest spoken-comprehension gap for post-Genki learners: they are listening for か to identify questions, and it is almost never there.

How the transformation works

Take any plain-form statement and raise the intonation at the end. That is the question. No particle is added. In writing, this is represented by a question mark (？), but in speech it is purely prosodic. The listener identifies the utterance as a question from the pitch rise on the final mora. か can still appear in casual speech in certain fixed expressions (どうするか) and in indirect questions (何時に来るか分からない), but as a sentence-final question marker between friends, it is absent.

Examples

[casual / friend asks if you're going to the party] 明日行く？ You going tomorrow?

[casual / checking if a friend has eaten] もうご飯食べた？ Have you eaten already?

[casual / at a store with a friend, pointing at something] これ、いい？ Is this one okay?

[casual / combined with 〜の question marker for softer nuance (→ 1.10)] 大丈夫？疲れてない？ You okay? Not tired?

[casual / confirming a plan] じゃあ３時でいい？ So three o'clock works?

[for comparison — か on plain form sounds aggressive] 何してるか。 What are you doing? (sounds like a demand / interrogation)

Dialogue

[casual / friends meeting up, A female, B female]

A: あ、来た。待った？　[Oh, you're here. Did you wait long?]

B: ううん、今来たとこ。どこ行く？　[Nah, I just got here. Where are we going?]

A: 駅前に新しいカフェできたんだけど、知ってる？　[A new cafe opened by the station — you know about it?]

B: あ、インスタで見た。行ってみよう。　[Oh, I saw it on Instagram. Let's check it out.]

Contrast with

1.1: だ（述語） — statement with falling intonation vs. question with rising intonation on the same sentence

Written note

→ See Appendix C.1 for particle drop in written questions (明日暇？ in LINE messages).

1.10 〜の？ / 〜の

← 教科書の形: 〜ですか

Formula: [S (plain)] + ∅？ → [S (plain)] + の？

Register: ★★★ core; feminine tendency in declarative 〜の Medium: spoken — all

Gap Note

Genki II introduces 〜んですか as a question form that seeks explanation, but the plain equivalent 〜の？ receives little attention in model dialogues. Minna no Nihongo similarly underserves this form. The result is that learners hear 何してるの？ and are unsure how it differs from 何してる？ — both are casual questions, but 〜の？ carries an added layer: it signals that the speaker is personally interested, seeking context, or mildly surprised. It is not just "what are you doing?" but closer to "what are you doing (I want to know the story)." Additionally, 〜の as a sentence-final declarative (not a question) has a feminine tendency that learners often do not recognize.

How the transformation works

Attach の to the end of a plain-form clause to form a question (with rising intonation) or a soft explanatory statement (with falling intonation). Before の, だ becomes な: 学生だ → 学生なの？, 元気だ → 元気なの？. Verbs and い-adjectives attach directly: 行くの？, 高いの？. The question version (〜の？) is gender-neutral. The declarative version (〜の with falling intonation) has a feminine tendency in Tokyo speech — male speakers more commonly use 〜んだ (→ 3.1) in the same position.

Examples

[casual / friend sees you packing a bag] どこか行くの？ Are you going somewhere?

[casual / surprised that a friend quit their job] え、辞《や》めたの？ Wait, you quit?

[casual / female speaker, soft declarative, explaining why she's tired] 今日、朝からずっと走ってたの。 I was running all morning.

[casual / parent to child, gentle question] 宿題《しゅくだい》もう終わったの？ Are you done with your homework already?

[casual / friend noticed you're not eating, with concern] 食べないの？おいしいよ。 You're not eating? It's good.

Dialogue

[casual / two friends at a park, A female, B female, B arrives looking upset]

A: どうしたの？なんか元気ないね。　[What's wrong? You seem kind of down.]

B: ちょっとね。仕事で失敗しちゃって。　[A little bit. I made a mistake at work.]

A: そうなの？大変だったね。　[Really? That must've been rough.]

B: まあ、もう終わったことだし。気にしないようにする。　[Well, it's already over and done with. I'll try not to worry about it.]

A: うん、そうしな。お茶でも飲もうよ。　[Yeah, do that. Let's grab some tea or something.]

Variations

〜のか（masculine question） Formula: [S (plain)] + のか

[casual / male speaker, somewhat rough, reacting to information] え、そうなのか。知らなかった。 Oh, is that so. I didn't know.

Contrast with

1.9: 〜？（上昇調） — bare intonation question is neutral; の？ adds personal investment or surprise

道 — Colloquial Japanese Patterns