〜ことだ

Pattern: 〜ことだ
Level: N2
Meaning: Should / must (advice or suggestion)
Attaches to: Verb (dictionary form or ない-form)
Example: 健康のために、毎日運動することだ。 For your health, you should exercise every day.
Easily confused with: 〜ほうがいい: 'ほうがいい' is a suggestion, 'ことだ' sounds more like authoritative advice.