Every Japanese auxiliary is fussy about which base it attaches to. ない demands the 未然形 (書か-); たい demands the 連用形 (書き-); らしい demands the plain 終止形 (書く). Grammar references specify this attachment by the classical base name — "接続（せつぞく）: 連用形" — and once you can read that code, you can predict any form. This page is the master cross-reference: each auxiliary lined up against the base it rides, worked through 書く, plus the one auxiliary that means two opposite things depending on the base — そうだ.
If the six base names (未然・連用・終止・連体・仮定・命令) are not yet automatic, read the six bases first. This page assumes them and puts them to work.
The master attachment table
| Auxiliary | Meaning | Base | 書く result |
|---|---|---|---|
| ない | negative | 未然形 (書か) | 書かない |
| れる／られる | passive / potential | 未然形 (書か) | 書かれる |
| せる／させる | causative | 未然形 (書か) | 書かせる |
| ず | negative (literary) | 未然形 (書か) | 書かず |
| う／よう | volitional | 未然形 (書こ sub-form) | 書こう |
| ます | polite | 連用形 (書き) | 書きます |
| た | past | 連用形 (＋音便) | 書いた |
| たい | desiderative | 連用形 (書き) | 書きたい |
| ながら | while | 連用形 (書き) | 書きながら |
| そうだ (様態) | looks about to / appears | 連用形 (書き) | 書きそうだ |
| らしい | it seems / apparently | 終止形 (書く) | 書くらしい |
| そうだ (伝聞) | I hear that | 終止形 (書く) | 書くそうだ |
| だろう／でしょう | probably | 終止形 (書く) | 書くだろう |
| ようだ | seems / appears | 連体形 (書く) | 書くようだ |
| まい | won't / negative resolve (literary) | 終止形 (書く) | 書くまい |
| ば | conditional "if" | 仮定形 (書け) | 書けば |
| （命令） | imperative | 命令形 (書け) | 書け |
Notice the pattern the table exposes: the 未然形 (書か-) is the launchpad for everything irrealis — negation, passive, causative, volitional; the 連用形 (書き-) carries the continuative endings — politeness, past, desire; and the 終止/連体形 (書く) hosts the evidential and modal particles — らしい, hearsay-そう, だろう, ようだ. The base you pick is a socket, and the auxiliary is the plug.
このままでは、締め切りに間に合わないかもしれない。
kono mama de wa, shimekiri ni maniawanai kamoshirenai
At this rate, we might not make the deadline. (未然形 間に合わ ＋ ない)
昨日の会議で、新しい方針が発表された。
kinō no kaigi de, atarashii hōshin ga happyō sareta
A new policy was announced at yesterday's meeting. (未然形 ＋ passive された)
部長は部下に、週末まで残業させたらしい。
buchō wa buka ni, shūmatsu made zangyō saseta rashii
Apparently the department head made his staff work overtime right through the weekend. (未然形 ＋ causative させた, plus 終止形 ＋ らしい)
The crux: そうだ means opposite things on different bases
This is why the page exists. The string そうだ attaches to two different bases, and the base flips its meaning:
- 様態（ようたい）そうだ — "looks about to / appears" — rides the 連用形 (the ます-stem). It reports what your own eyes judge.
- 伝聞（でんぶん）そうだ — "I hear / they say" — rides the 終止形 (the plain dictionary form). It reports secondhand information.
| 様態 そうだ (appearance) | 伝聞 そうだ (hearsay) | |
|---|---|---|
| Base | 連用形 (stem) | 終止形 (plain form) |
| 降る | 降りそうだ — looks about to rain | 降るそうだ — I hear it'll rain |
| i-adjective 高い | 高そうだ (drop い) | 高いそうだ |
| na-adjective 元気 | 元気そうだ | 元気だそうだ |
空が真っ暗だ。今にも雨が降りそうだ。
sora ga makkura da. imanimo ame ga furisō da
The sky's pitch black — it looks like it could rain any second now. (様態: 連用形 降り ＋ そうだ)
天気予報によると、明日は一日中雨が降るそうだ。
tenki yohō ni yoru to, ashita wa ichinichijū ame ga furu sō da
According to the forecast, it'll rain all day tomorrow. (伝聞: 終止形 降る ＋ そうだ)
The evidential neighbours: らしい, ようだ, だろう
らしい, ようだ, and だろう all sit on the plain form too, and all shade "it seems / probably," but with different sources and confidence:
田中さん、来月で会社を辞めるらしいよ。
tanaka-san, raigetsu de kaisha o yameru rashii yo
Word is Tanaka's leaving the company next month. (終止形 辞める ＋ らしい — hearsay/rumor)
返事がないな。どうやら、道に迷ったようだ。
henji ga nai na. dōyara, michi ni mayotta yō da
No reply — looks like they've gotten lost. (連体形 迷った ＋ ようだ — inference from evidence)
あれだけ勉強したんだから、彼はきっと合格するだろう。
are dake benkyō shita n da kara, kare wa kitto gōkaku suru darō
After studying that much, he'll surely pass. (終止形 合格する ＋ だろう — conjecture)
Note that ようだ technically rides the 連体形 — which for verbs is identical to the 終止形 (書く), but shows up with な-adjectives: 元気なようだ, not ×元気だようだ. That is the one place the 終止形／連体形 distinction still bites.
The 仮定形 and the literary bases
ば is the lone tenant of the 仮定形 (書け): 書けば, 急げば, 行けば. And two literary auxiliaries round out the table — ず (negative, on the 未然形: 書かず, and fossilized in 思わず, 絶えず) and まい (negative volitional / firm refusal, on the 終止形: 二度と行くまい). (register: literary / formal for both.)
今すぐ急げば、終電にまだ間に合う。
ima sugu isogeba, shūden ni mada maniau
If you hurry right now, you can still catch the last train. (仮定形 急げ ＋ ば)
あんな失礼な店には、二度と行くまい。
anna shitsurei na mise ni wa, nido to iku mai
I shall never set foot in such a rude shop again. (終止形 行く ＋ まい, literary)
Common mistakes
1. Putting 様態 そうだ on the plain form. To say "looks about to rain," the base is the stem 降り-, not 降る-.
❌ 空が暗い。雨が降るそう。
Wrong for 'looks about to rain' — 様態 そうだ rides the 連用形: 降りそう. 降るそう(だ) is hearsay, 'I hear it'll rain.'
✅ 空が暗い。雨が降りそう。
sora ga kurai. ame ga furisō
The sky's dark — it looks like rain.
2. Putting 伝聞 そうだ on the stem. To report hearsay, keep the whole plain form.
❌ 予報では、明日は晴れそうだ。
If you mean 'the forecast says it'll be clear,' that's hearsay — keep the plain form: 晴れるそうだ. 晴れそうだ means 'it looks like it'll clear up' (your own judgment).
✅ 予報では、明日は晴れるそうだ。
yohō de wa, ashita wa hareru sō da
The forecast says it'll be sunny tomorrow.
3. Attaching ない to the 連用形. Negation rides the 未然形 (書か-), not the ます-stem (書き-).
❌ 私は普段、日記を書きない。
Wrong — ない attaches to the 未然形 書か, not the 連用形 書き: 書かない.
✅ 私は普段、日記を書かない。
watashi wa fudan, nikki o kakanai
I don't usually keep a diary.
4. Forgetting the さ-insertion on 良い／無い before 様態 そう. These two i-adjectives insert さ: 良い→良さそう, 無い→無さそう.
❌ この店、雰囲気が良そうだね。
Wrong — 良い inserts さ before 様態 そう: 良さそう. (Plain 高い just drops い → 高そう, but 良い・無い are the exceptions.)
✅ この店、雰囲気が良さそうだね。
kono mise, fun'iki ga yosasō da ne
This place looks like it has a nice atmosphere.
Key takeaways
- Auxiliaries attach by base: 未然形 (書か) takes ない・れる・せる・う; 連用形 (書き) takes ます・た・たい・様態 そう; 終止/連体形 (書く) takes らしい・伝聞 そう・だろう・ようだ; 仮定形 (書け) takes ば.
- そうだ is two auxiliaries: 様態 (appearance) rides the 連用形 (降りそう), 伝聞 (hearsay) rides the 終止形 (降るそうだ) — same string, opposite base, opposite meaning.
- The 未然形 = irrealis hub, the 連用形 = continuative hub, the 終止/連体形 = evidential/modal hub — the table's rows cluster by exactly these three.
- Watch the small traps: 良い・無い insert さ before 様態 そう (良さそう), and ようだ needs な with na-adjectives (元気なようだ).
Now practice Japanese
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Start learning Japanese→Related Topics
- Classical 活用: The Six Bases (Bridge Page)N2 — The traditional six 活用形 — 未然・連用・終止・連体・已然/仮定・命令 — worked through 書く and mapped onto the modern forms this guide teaches, so you can read any 活用表 or grammar reference that still uses the classical labels.
- All Forms, All Classes: Master ChartN4 — The one-sheet everything reference — every major verb form (dictionary through causative-passive, volitional, conditional, imperative) down the side and 書く・食べる・する・来る across the top, so you can verify any form without hunting across pages.
- Classical Negatives ぬ・ず・まい: TableN2 — The reference for the negatives that survive from classical Japanese into formal and written modern usage — 〜ぬ／〜ん, 〜ず／〜ずに, and the negative-volitional まい — with the irregular せず・来ず and the 知らん-vs-知らぬ register split.