食べたそうだ vs. 食べそうだ, 静かだそうだ vs. 静かそうだ

Question

I saw this as a comment on this question, Why does そう in 「美味しいそう」 not mean "seem" the way I think it should?「美味しいそう」-not-mean-seem-the-way-i-think-it-should,

and would love to understand the differences.

I am sure I will mangle the translation, so forgive me.

食べたそうだ Looks like he ate it.

食べそうだ Looks like he will eat it.

静かだそうだ I heard that it's quiet.

静かそうだ Seems quiet.

If anyone would be kind enough to explain the differences in meaning and usage, I would greatly appreciate it. I didn't learn how to embed the quoted question, so sorry again for that.

Answer 1

The first そう comes after 終止形 of verbs and adjectives. All 終止形 forms, negatives, passives, causatives, present and past etc are possible.

This means "I hear(d)/read that... " (not looks/seems like as assumed in the question).

彼は死んだそうだ I heard he died
あのケーキは美味しいそうだ I hear that cake is declicious
彼は嫌われていなかったそうだ They say he wasn't hated.

This そう is often listed as a particle, but it really behaves like a noun, and is almost always followed by copula. It has no 連体形, i.e. 静かだそうな is ungrammatical (unless な is the sentence-ending particle). Also, the following copula is not used in the past tense, i.e. 静かだ(った)そうだった does not exist, but 静かだったそうだ does.

The second そう comes after the 連用形 of verbs and the stem of adjectives. 良い(いい) and 無い have irregular forms 良さそう and 無さそう. Negative verb forms ～ない become ～なそう, but ～なさそう is often heard, although it's considered incorrect.

濃{こ}そう, 静かそう, 行きたそう, 食べなそう looks dense, seems quiet, looks like sby wants to go, looks like sby won't eat

The result of this is a na-adjective meaning "looks ..." or "seems ...". For action and state-change verbs, it can also meen "about to ..." or "looks like sby will ...".

Being a na-adjective, this form can be used both in the 終止形 and 連体形 forms (and negative forms etc.),

美味しそうなケーキ a delicious-looking cake
このケーキは美味しそうだ this cake looks declicious

死にそうな人 a person (looking like he's) about to die
彼は死にそうだ (he looks like) he's about to die

Answer 2

The そう that takes an appositive clause is a formal noun (although in traditional grammar, it is not called so). It has reference to a general situation that one heard from someone else. Or, it may be considered a sentence ending. This happens in syntax.

[寒い]そうだ
'What I heard is that it is cold.'

[食べた]そうだ
'What I heard is that she ate it.'

[静かだ]そうだ
'What I heard is that it is quiet.'

[日本人だ]そうだ
'What I heard is that the person is a Japanese.'

The -そう that attaches to a verb stem, adjective stem or an adjectival noun (a.k.a. na-adjective, 形容動詞語幹) is an affix that derives a na-adjective that means just about to. likely to, it looks like. This happens in morphology.

[寒そう]だ
'It looks cold'

[食べそう]だ
'She is just about to eat it.'

[静かそう]だ
'It seems to be quiet.'

It does not attach to a noun. In order to express a similar meaning with a noun, you can use っぽい.

日本人っぽい
'The person looks like a Japanese.'

Since that latter -そう derives a adjectival noun, it can be used to modify a noun.

[寒そう]な部屋
'a room that looks cold'

[食べそう]なもの
'things that she is likely to eat'

[静かそう]な物件
'a real estate in a quiet environment'