used as そうだ, it is Auxiliary verb. Apparently not just copula. tl:dr; unaltered/unconjugated or だそうだ → hearsay, information repeated from someone else conjugated → it seems that (...)
そうだ vs らしい vs みたい vs ようだ vs なんだって
seems (...)
The broad meaning in each of its applications is that something 'seems' to be a certain way. It implies low confidence This conjugates with verbs, 形容詞. In 形容動詞, no だ is added.
It can be used with a verb conjugation after the stem
あの建物は崩れそうだ It looks like that building is about to collapse.
彼は病気になりそうだ He looks like he will become sick.
彼女は毎日走りそうだ。 She looks like she runs every day.
Also with形容動詞＋
あの店員は丁寧そうだ。 The clerk appears to be polite.
電話はとても便利そうだ。 Phones seem super convenient!
It can be used with a形容詞〜 . Note that the extra い disappears!
これは正しそうだ This appears to be correct.
楽しそうです Fun-looking
このケーキは美味しそうじゃありません This cake doesn't look yummy at all...
Negative: なさそう
When negative, it has a special conjugation 〜なさそう. This is due to the ない that is used with negative verbs being an auxiliary verb, and not an い-Adjective.
彼の部屋は汚くなさそうだ。 His room doesn't seem messy
あの車は小さくて便利じゃなさそう。 That car is too small, and it doesn't seem convenient.
This is NOT the case for verbs
彼はもうイギリスに帰らな~~さ~~そうだ。
Negative: そうにもない
Other negative is a Common sentence pattern too: そうにもない is the negative version of 「〇〇そうだ。」, used to denote that something 'doesn't look like it is (...)', or 'does not look to be (...)'
雨が降りそうにもない。 It doesn't look like it will rain
Hearsay
Hearsay information repeated from someone else, or making a presumption No conjugation, just add そうだ to the end.
forverb＋
あの建物は崩れたそうだ I heard that the building has collapsed.
彼女は毎日走るそうだ。 Rumour has it that she she runs every day.
形容動詞＋, an extra だ needs to be added.
あの店員は丁寧だそうだ。 I've heard that the clerk is polite.
Unlike the 'seems-like' interpretation, hearsay can also gonoun＋ .
先輩は明日も仕事だそうだ I've heard that senpai will be working tomorrow as well...
Sometimes it is combined with some variation of 言う to denote who said it. 彼が言うには、 明日学校は休みだそうです。 According to him, apparently tomorrow is a day off for school.
Also with 話Method or means
先生の話では、田中さんは体調が悪いそうです。 Sensei said that Tanaka-san's health is bad.