In short

There are two そう, and only the attachment point tells them apart. Stuck on a stem it means “looks like, is about to” - what your eyes report: 雨が降りそうです (Ame ga furisō desu, it looks like rain). Stuck on a full plain form it means “I hear that” - what someone else told you: 雨が降るそうです (Ame ga furu sō desu, they say it’s going to rain). One kana of difference, two completely different claims.

The rule

The traditional names are worth knowing because they keep the two apart in your head: 様態 (yōtai, “appearance”) for the eyewitness そう, and 伝聞 (denbun, “report”) for the hearsay そう.

Step 1 - The split is mechanical, so learn the attachment, not the meaning.

Ask one question: did I cut the word down before adding そう?

• Cut it down to a stem -> 様態, appearance. 降り + そう, おいし + そう.
• Left it whole, including だ -> 伝聞, hearsay. 降る + そう, おいしい + そう, 学生だ + そう.

Step 2 - 様態: attach そう to the stem.

• Verbs: ます-stem + そう. 降ります -> 降り -> 降りそうです furisō desu (it looks like it will rain); できます -> でき -> できそうです dekisō desu (it looks doable); 落ちます -> 落ちそうです ochisō desu (it’s about to fall). With verbs the meaning is imminence (“about to happen”) or likelihood (“looks like it will work”).
• い-adjectives: drop い, add そう. おいしい -> おいしそう oishisō (looks tasty); 高い -> 高そう takasō (looks expensive); 忙しい -> 忙しそう isogashisō (looks busy).
• な-adjectives: the bare stem + そう. 元気（な）-> 元気そう genkisō (looks well); 静か（な）-> 静かそう shizukasō (looks quiet). No な, no だ.
• Two irregulars, both of which insert さ. いい -> よさそう yosasō (looks good), and ない -> なさそう nasasō (looks like there isn’t any). ×いそう and ×なそう are wrong in careful Japanese.

Step 3 - 様態そう then lives on as a な-adjective.

This is the payoff of the split: the appearance そう is not the end of the sentence, it is a new adjective, and it takes the full な-adjective set from lesson 8. おいしそうです (predicate), おいしそうでした (past), おいしそうなケーキ (before a noun), おいしそうに食べます (before a verb, as an adverb).

Step 4 - The negative of 様態そう has its own shape for verbs.

For verbs, “it doesn’t look like it will happen” is 〜そうにない or 〜そうもない, not ×〜そうじゃない: 雨が降りそうにないです／降りそうにありません ame ga furisō ni nai desu / furisō ni arimasen. For adjectives, negate the adjective first and let it end in ない, which then becomes なさそう: おいしくない -> おいしくなさそう oishikunasasō.

Step 5 - 様態そう does not attach to nouns, and does not state the obvious.

A noun cannot take it at all: ×あの人は男そうです is not Japanese, because 男 is a noun and because you can simply see that. 様態そう is for a property you infer from surface evidence, so it also resists adjectives naming something plainly visible - a red thing is 赤いです, not ×赤そうです. If you want “that person seems to be a student”, you need ようだ or らしい, not そう.

Step 6 - 伝聞: attach そうだ to the whole plain form, だ included.

Nothing is cut off here. Take the plain form from lesson 17 exactly as it stands and add そうです: 降るそうです, 降ったそうです, 降らないそうです, おいしいそうです, 静かだそうです, 学生だそうです. The だ that でしょう deletes (lesson 32) is kept here - that だ is the visible sign that you are relaying, not observing.

Step 7 - 伝聞そうだ is frozen.

It has no life of its own. It cannot take tense (×降るそうでした), it has no negative (×降るそうじゃないです), it never modifies a noun (×降るそうな天気), and it never becomes そうに. Any tense or negation you need goes inside, on the plain form: I hear it didn’t rain = 降らなかったそうです. The only thing that varies is politeness: そうです／plain そうだ.

Step 8 - Name your source.

Because 伝聞 relays someone else’s words, Japanese usually says whose: 〜によると (ni yoru to, according to) for an authority, 〜の話では (no hanashi de wa, from what X says) for a person. 天気予報によると……降るそうです。／田中さんの話では……安いそうです。

What this lesson is not. ようだ, みたいだ and らしい also come out as “seems / apparently” in English, and らしい in particular overlaps with hearsay そうだ. They are inference and resemblance based on indirect evidence, and they belong to lesson 49. Pure guessing with no evidence at all is でしょう and かもしれない, in lesson 32.

Forms & patterns

The attachment contrast - this table is the lesson.

様態そう inflects like a な-adjective; 伝聞そう inflects not at all.

Negative 様態 by class.

Minimal pairs - listen for the extra kana.

Examples

Common mistakes

• 雨が降りますそうです。 (Ame ga furimasu sō desu.) -> 雨が降るそうです。 (Ame ga furu sō desu.) - hearsay そうだ attaches to the plain form. Politeness is carried once, by そうです at the end.
• おいしいそうなケーキ (oishii sō na kēki) -> おいしそうなケーキ (oishisō na kēki) - for the “looks like” meaning the い-adjective loses its い. Keeping い gives the hearsay そう, which cannot modify a noun at all.
• この本はいいそうです。 meaning it looks good -> この本はよさそうです。 (Kono hon wa yosasō desu.) - いい becomes よさそう. いいそうです can only mean I hear it’s good.
• あの人は学生そうです。 (Ano hito wa gakusei sō desu.) -> あの人は学生のようです。 (Ano hito wa gakusei no yō desu.) - 様態そう never attaches to a noun, so an inference from a noun has to go to ようだ／らしい (lesson 49). If instead you are relaying what you were told, that is あの人は学生だそうです。 (Ano hito wa gakusei da sō desu.) - a different claim.
• 雨が降るそうでした。 (Ame ga furu sō deshita.) -> 雨が降ったそうです。 (Ame ga futta sō desu.) - 伝聞そうだ has no past. Put the tense inside, on the plain form.

Tips

• Count the kana. おいしそう = I can see it. おいしいそう = I was told. Same for な-adjectives, where the giveaway is だ: 元気そう (seen) vs 元気だそう (heard). One kana is the whole difference between an eyewitness and a rumour.
• Appearance そう keeps going; hearsay そう stops the sentence. If you ever need そうな, そうに, そうでした or そうにない, you are in the 様態 world by definition - the hearsay one is always the last thing you say, and it never bends.
• Do not build the verb negative with じゃない. ×降りそうじゃないです feels wrong to natives; the fixed forms are 降りそうにない and 降りそうもない (polite 降りそうにありません). Adjectives are the opposite - they go through なさそう: 高くなさそう.
• 伝聞そうだ makes you a messenger, not a witness. You take no responsibility for the claim, which is why it so often names a source (〜によると, 〜の話では) and why you cannot ask a question with it. It is also why you must not use it for your own hunch - a hunch is でしょう, かもしれない or ようだ.