(Verb masu stem) + sou 降りそう furisou = seems it will rain
(i-Adj base) + sou 美味しそう oishisou = seems delicious
(na-Adj base) + sou 暇そう himasou = seems to have time
With negatives the -nai becomes -nasa： 降らなさそう furanasasou = seems like it won't rain
= look; look like; appear; seem; feel like -auxiliary adjective which indicates that what is expressed by the preceding sentence is THE SPEAKER'S CONJECTURE concerning an event in the future/ present state of someone/ sth (never a past state/event), BASED ON WHAT THE SPEAKER SEES OR FEELS. -used only when the speaker directly observes sth -cannot be used to express the speaker's conjecture concerning a past event/ state -Noun/ Noun+ copula cannot precede sou da (in this case we use rashii), but N+copula neg/nonpast can: ex: a)* 加藤さんは学生そうだ。 b)* 加藤さんは学生だそうだ。=Mr Katou looks like a student. c)加藤さんは学生じゃなさそうだ。=Mr Katou doesn't look like a student。 - in this construction, the negative form of verbs usually don't precede sou da. Instead, Vmasu sou ni/ mo nai is used: a) 彼は車を売りそうに・もない。＝ He doesn't seem to sell his car. b) この問題は学生は出来そうに・もない。= It doesn't seem that the students can solve this problem. -also used to express the speaker's conjecture concerning his own non-volitional future actions based on what he feels: a)僕はこのケーキを残しそうだ。＝I'm affraid I can't eat all this cake. b)私はとても疲れていてたおれそうだ。=I'm so tired that I feel weak (lit:like I'm falling down) - sou da is a NA Adjective; the prenominal form is SOU NA: a) 高そうな車＝a car which looks expensive/ an expensive-looking car b)雨が降りそうな空＝(lit:) the sky which looks like it will bring rain
Beware forming this construction with かわいい （可愛い）. かわいそう（可哀相） does not mean "looks cute", but "pathetic" or "pitiful", as my friend managed to find out to his chagrin.
Appparently the [sou] ending can be used to connotate both heard and seems: 負けるそう makeru-sou desu = I heard he will lose 負けそうです make-sou = seems he will lose
One more rule/example: If you want to say いい + そう (looks good) then you need to use よさそう
I added a See Also to よう... Unless I am mistaken if you want to use a noun, you use N + のよう (e.g. 先生のよう). But, for a negative you use N + ではなさそう (e.g. 先生ではなさそう) Also, somewhere I read that the negative for a verb is V (ます form) + そうもありません NOT the そう followed by ではありません mentioned in the first comment. Is this true? As for V-tai form I think たい acts like A1 adjective. いい uses よい instead (e.g. よさそう / よくなさそう) Finally, note that そう acts as な-adj (you can probably guess this from the examples but I thought I would state it explicitly). Any corrections very welcome...
そう followed by ではありません can be used. I added eg. What is A1 adjective?
ex#3258 I think これは食べられそうではありません。is fine. When 思いません is followed, これは食べられるとは思いません。would be better.
Possibly the '不機嫌そう' use in the example is another way of distinguishing between what you can actually know (whether somebody sounds grumpy) vs what only they know (how they feel).
watch out with きそう, it sounds too close to くそ
hmm Do you mean くそ is the one「きそう、(-.-;) くる、くる I have to go to the bathroom」? Or くそ！くそっ！ Both are the same in English, too でしょ？
ex#3137 KS is too good at Kanji. Usually we use うどん.
In the real world, nobody would confuse between 来そう and くそ.
来るそう = I heard he will come きそう = it seems he will come
Negative can also be formed by +ve そう followed by ではありません (etc.) 美味しそうじゃないよ！ "It doesn't look tasty!"