-sou ～そう - Suffix | Japanese with Anime

In Japanese, when sou そう is a suffix, it means something "seems" to be somehow, or that you've "heard from someone" that it was somehow.

It Seems

When the sou そう suffix means "it seems," it's attached to the stem of i-adjectives, the noun form of verbs, and the stem of auxiliaries, too.

futsuu-sou 普通そう
Seems normal.
- futsuu 普通
  Normal. (no-adjective.)
kirei-sou 綺麗そう
Seems pretty.
- kirei 綺麗
  Pretty. (na-adjective.)
oishi-sou 美味しそう
Seems delicious.
- oishii 美味しい
  Delicious. (i-adjective.)
ochi-sou 落ちそう
Seems [it will] fall.
- ochiru 落ちる
  To fall. (verb.)
kate-sou 勝てそう
Seems [I] can win.
- kateru 勝てる
  To be able to win. (potential form.)
- katsu 勝つ
  To win.
katena-sou 勝てなそう
Seems [I] can not win.
- katenai 勝てない
  To not be able to win. (negative form of potential.)
yarita-sou やりたそうだ
Seems [he] wants to do [it].
- yaritai やりたい
  To want to do. (tai-form.)
- yaru やる
  To do.

Irregular Words

There are two exceptions, two adjectives that normally get sou そう attached to their sa-forms, rather than to their stem.

yosa-sou よさそう (or 良さそう)
Seems good.
- yosa よさ
  Good-ness.
- yoi よい
   ii いい
  Good.
nasa-sou なさそう (or 無さそう)
Seems nonexistent.
Seems lacking. Seems to not have. Seems to not exist.
- nasa 無さ
  Nonexistent-ness.
- nai 無い
  Nonexistent.

なそう vs. なさそう

The word nai ない has multiple functions in Japanese. When it's attached to another words to put them in their negative forms, it becomes na-sou なそう, but when it simply acts as an adjective, it's nasa-sou なさそう.

okane ga nai
お金が無い
Money is nonexistent.
[That guy] doesn't have money.
okane ga nasasou da
お金が無さそうだ
Money seems nonexistent.
[That guy] seems to not have money. (he looks poor.)
moenai
燃えない
To not burn.
moena-sou
燃えなそう
Seems to not burn. (it doesn't appear to be combustible.)

そうな

The sou そう suffix can be inflected like a na-adjective. This works by using the na な particle, that acts as an attributive copula, replacing the predicative copula da だ, and making the relative clause sou na そうな.

oishii keeki
美味しいケーキ
Delicious cake.
oishi-sou da
美味しそうだ
It is delicious-seeming.
It seems delicious.
{oishi-sou na} keeki da
美味しそうなケーキだ
It is a cake [that] {is delicious-seeming}.
It is a cake [that] {seems delicious}.

Note that using sou そう in this manner turns the adjective into an assumption. In oishi-sou na keeki, you assume the cake is delicious. In oishii keeki, you assert that it is delicious, as you have either eaten it already or you have confidence about it.

そうに

Like any na-adjective, sou そう can be converted to adverbial form with the ni に particle, that acts as an adverbial copula.

{oishi-sou ni} taberu
美味しそうに食べる
To eat it {in a way that is deliciously-seeming}.
To eat it deliciously-seeming.
To eat it like it's delicious.

Again, this is a mere guess of the speaker based on how things look. Someone could be eating something they dislike, but the speaker could be imagining they're loving it for some reason.

Furthermore, "seeming" isn't limited to how things look. It could be to how they sound, smell, and so on.

{ita-sou na} kao
痛そうな顔
A face [that] {is painful-seeming}..
A face [that] {looks painful}.
A painful face.
A painful expression.
{ita-sou ni} kikoeru
痛そうに聞こえる
To be heard {in a way that is painful-seeming}.
To be heard painfully-sounding.
To sound like it's painful.

Manga: Kaguya-sama wa Kokurasetai ~Tensai-Tachi no Ren'ai Zunousen かぐや様は告らせたい～天才たちの恋愛頭脳戦～ (Chapter 6, 白銀御行は隠したい)

Context: a guy was asked:
- kanojo ga iru?
  彼女が居る
  Do [you] have a girlfriend?
kanojo inai tte~~!
彼女居ないってー！
[He] said "[he] doesn't have a girlfriend"!
isou ni nai mon ne~~!
居そうに無いもんねー
[He] doesn't seem [he] would have [one], right~~
- Here, a second girl says the guy doesn't looks like he would have a girlfriend. She's judging him by his appearances.
- mon もん
  (nominalizer.)
- ne ね
  Right?
chou ukeru!
超ウケル！
[That's] super funny!
- ukeru 受ける
  To receive. (literally.)
  To find funny. (slang.)
fufu'
ふふっ
*giggle*

I heard

Another way the sou そう suffix is used is to say you've heard that something was somehow.
To have an idea of the differences:

oishii-sou da
美味しいそうだ
I heard that it is delicious.
oishi-sou da
美味しそうだ
It looks delicious.

With i-adjectives, whether the -i ～い remains or the suffix is attached to the stem changes the function of sou そう.

With verbs the difference is more obvious. The "seems" meaning often implies something hasn't happened yet, it just seems it will, can, or is maybe is happening. The "I heard" meaning, on the other hand, is often used with things that already happened.

shini-sou da
死にそうだ
[He] seems [he] will die.
- Oh no! Someone help!
shinda-sou da
死んだそうだ
I heard [he] died.
- Welp. Nothing we can do anymore.

だそうだ

The way sou そう is used resembles a noun. In particular, it resembles the light noun you よう. However, sou そう is not a noun, it's a suffix.

We know this because phrases ending with the predicative copula da だ can get sou そう suffixed right after them. If it was a noun, da だ would turn into the attributive na な copula in order to create a relative clause to qualify it.

kanojo wa neko ga suki da
彼女は猫が好きだ
As for her, cats are liked.
She likes cats.
kanojo wa neko ga suki da-sou da
彼女は猫が好きだそうだ
As for her, cats are liked, I heard.
I heard that she likes cats.
- I heard it from someone.
kanojo wa {neko ga suki na} you da
彼女は猫が好きなようだ
As for her, it's the guess [that] {cats are liked}.
I think she likes cats.
- I'm not sure, but I'm guessing this is true.