歌い合う

Causative form (make/let do)

Past plain form

Te-form for connecting verbs

Negative plain form

Negative past

Negative te-form

Polite past

Polite present/future

Polite negative

Polite negative past

Volitional form (let's do)

Potential form (can do)

Passive form

Dictionary form, plain form

Conditional form (if)

Imperative/command form