Soon, suddenly, gradually
How soon something happens, from right away to 'it's about time', plus whether a change comes out of the blue or bit by bit.
sugu
right away, soon
すぐ
Makes an action immediate or close at hand (sugu iku, sugu kaeru). It also builds ima sugu and mou sugu.
sugu iku ne.
I'll be right there.
すぐ行くね。
sugu ikimasu.
I'll be right there.
すぐ行きます。
ima sugu means 'right this minute'. sugu can also mean 'easily' (sugu okoru = gets angry easily) and 'very near' (sugu soko = right over there, eki kara sugu = right by the station).
mou sugu
very soon, any minute now
もうすぐ
Says that a time or event is about to arrive, before a verb (mou sugu tsuku) or a noun (mou sugu natsu = summer's nearly here).
mou sugu tsuku yo.
I'm almost there.
もうすぐ着くよ。
mou sugu tsukimasu.
I'm almost there.
もうすぐ着きます。
It is about time only. 'Almost' as in nearly all is hotondo, and 'a little more' is mou sukoshi.
sorosoro
it's about time
そろそろ
Signals that it's time to move on, most often to leave (sorosoro kaeru). It softens wrapping things up.
sorosoro kaeru ne.
I'd better head home.
そろそろ帰るね。
sorosoro kaerimasu ne.
I'd better head home.
そろそろ帰りますね。
The polite way to excuse yourself is sorosoro shitsurei shimasu.
kyuu ni
suddenly
急に きゅうに
Marks an abrupt, unexpected change or action. kyuu ni dou shita no? means 'what's got into you?'
kyuu ni samuku natta ne.
It's suddenly turned cold, hasn't it?
急に寒くなったね。
kyuu ni samuku narimashita ne.
It's suddenly turned cold, hasn't it?
急に寒くなりましたね。
kyuu ni gomen ne = sorry for the short notice; kyuu na youji ga dekite = something came up (the standard excuse). totsuzen (stronger) and ikinari (casual, abrupt) are near-synonyms.
Learn alongside: dandan
dandan
gradually, more and more
だんだん
Says a state changes bit by bit. It almost always pairs with -ku naru / -ni naru, plus -te kita for change up to now (dandan wakatte kita = it's slowly starting to make sense) or -te iku for change from now on (dandan samuku natte iku). Learn natte kita (has been getting) as a chunk here; the -te kuru pattern itself comes later (-te kuru).
dandan samuku natte kita ne.
It's been gradually getting colder, hasn't it?
だんだん寒くなってきたね。
dandan samuku natte kimashita ne.
It's been gradually getting colder, hasn't it?
だんだん寒くなってきましたね。
dandan is for a change in degree (getting colder, getting used to it), not for doing something in small portions. For that, use sukoshi zutsu (sukoshi zutsu tabete, sukoshi zutsu oboeru). For 'slowly' as a speed (speak slowly), use yukkuri.