Choosing
Noun + particle frames for picking among options (deciding, settling, suggesting loosely) plus the frame for when only one option is left.
-de ii
polite -de ii desuX will do, X is fine
〜でいい 〜でいいです
After a noun, settles on it as good enough (mizu de ii, kore de ii?) when ordering, checking or accepting something.
koohii de ii yo.
Coffee's fine.
コーヒーでいいよ。
koohii de ii desu.
Coffee's fine.
コーヒーでいいです。
Can sound like 'it'll have to do'; koohii ga ii is the keen choice. To accept a host's offer, say koohii o onegai shimasu; kore de ii desu ka? (is this OK?) is always safe.
-ni suru
polite -ni shimasugo with, decide on
〜にする 〜にします
After a noun, picks it from the options (kore ni suru, raishuu ni suru), the standard way to order or settle a choice.
jaa, koohii ni suru.
OK, I'll have coffee.
じゃあ、コーヒーにする。
jaa, koohii ni shimasu.
OK, I'll have coffee.
じゃあ、コーヒーにします。
With a verb it becomes koto ni suru: iku koto ni shita = I decided to go.
-demo
... or something
〜でも
After a noun, offers it as one loose example so a suggestion sounds soft (ocha demo, eiga demo), mostly in invitations.
koohii demo nomu?
Want to grab a coffee or something?
コーヒーでも飲む？
koohii demo nomimasen ka?
Shall we grab a coffee or something?
コーヒーでも飲みませんか？
Three readings after a noun: a loose example in offers and invitations (ocha demo), 'even' (kodomo demo wakaru, sensei demo shiranai), and 'any-' after question words (nandemo ii). Only at the start of a sentence does demo mean 'but'.
-shika nai
polite -shika nai desuhave no choice but to
〜しかない 〜しかないです
After a plain verb, says it's the only option left (yaru shika nai, matsu shika nai), for resolve or resignation.
mou yaru shika nai.
I guess I just have to do it.
もうやるしかない。
mou yaru shika nai desu.
I guess I just have to do it.
もうやるしかないです。
After a noun it's plain 'only': kore shika nai = this is all there is. More formal: -shika arimasen.
Learn first: shika