Let's, suggestions & plans
The volitional -ou family for inviting and offering, the softer -nai? invitation and -tara? advice, then tsumori and -ou to omou for your own plans.
-ou / -you
polite -mashoulet's (do)
〜おう/〜よう 〜ましょう
The volitional form proposes doing something together (ikou, tabeyou, shiyou). Godan verbs change the final u to ou (iku → ikou, kaeru → kaerou); ichidan verbs swap ru for you (taberu → tabeyou).
issho ni ikou
Let's go together.
一緒に行こう
issho ni ikimashou
Let's go together.
一緒に行きましょう
The irregulars are suru → shiyou and kuru → koyou.
Learn alongside: -ou ka / -you ka, -nai?, -tara?
-ou ka / -you ka
polite -mashou kashall we / shall I?
〜おうか/〜ようか 〜ましょうか
Asks whether to do something together, or offers to do it for the listener (mado akeyou ka? = shall I open the window?).
issho ni ikou ka?
Want me to come with you?
一緒に行こうか?
issho ni ikimashou ka?
Shall I come with you?
一緒に行きましょうか?
With a falling tone it can be self-directed: jaa, kaerou ka (well, guess I'll head home).
Learn alongside: -ou / -you, -nai?, -tara?Learn first: -ou / -you
-nai?
polite -masen kawant to...? (invitation)
〜ない? 〜ませんか
Invites the listener with a rising negative question (issho ni ikanai?), which leaves room to decline. It is softer than -ou.
issho ni ikanai?
Want to come along?
一緒に行かない?
issho ni ikimasen ka?
Would you like to come along?
一緒に行きませんか?
The rising tone is what makes it an invitation; flat ikanai just means 'I'm not going.'
Learn alongside: -ou / -you, -ou ka / -you ka, -tara?Learn first: -nai
-tara?
polite -tara dou desu kawhy don't you...?
〜たら? 〜たらどうですか
Suggests, with a rising tone, something the listener could do for their own good (yasundara?, kiite mitara?). The fuller form is -tara dou?. -ba? (sureba?) is curter and can sound dismissive (katte ni sureba? = suit yourself).
chotto yasundara?
Why don't you take a break?
ちょっと休んだら?
chotto yasundara dou desu ka
Why don't you take a little break?
ちょっと休んだらどうですか
With superiors -tara dou desu ka can sound pushy; -ta hou ga ii kamo is gentler.
Learn alongside: -ou / -you, -ou ka / -you ka, -nai?Learn first: -tara
tsumori
polite tsumori desuintend to / plan to
つもり つもりです
States a plan you've already decided on. It attaches to the plain form (iku tsumori, ikanai tsumori).
kyou wa hayaku neru tsumori
I'm planning to go to bed early tonight.
今日は早く寝るつもり
kyou wa hayaku neru tsumori desu
I plan to go to bed early tonight.
今日は早く寝るつもりです
After a past verb it means 'I thought I had': itta tsumori = I thought I'd said it. Asking others about their tsumori can sound like a challenge (dou iu tsumori? = what do you think you're doing?), so ask about plans with ...suru no? / ...n desu ka. For loose plans, -ou to omotteru is softer.
Learn alongside: -ou / -you to omou
-ou / -you to omou
polite -ou / -you to omoimasuI'm thinking of (doing)
〜おう/〜ようと思う 〜おう/〜ようとおもう 〜おう/〜ようと思います
Shares a plan you're deciding on now or are still considering. It is softer than tsumori.
kyou wa hayaku neyou to omou
I think I'll go to bed early tonight.
今日は早く寝ようと思う
kyou wa hayaku neyou to omoimasu
I think I'll go to bed early tonight.
今日は早く寝ようと思います
Polite speech keeps the plain volitional (neyou to omoimasu, never *nemashou to omoimasu); -ou to omotteru = I've been thinking of it.
Learn alongside: tsumoriLearn first: -ou / -you, to omou