At a glance
～上は means "now that" or "since". It shows that because the speaker has decided or done something, a certain resolve or duty follows.
Verb (dictionary form / た-form) + 上は、[resolve / obligation / advice]
約束した上は、必ず守ります。 Now that I've promised, I will definitely keep my word.
How to form it
上は attaches to the plain form of a verb:
| Attaches to | Form | Example | Register |
|---|---|---|---|
| Verb, dictionary form | 引き受ける + 上は | 引き受ける上は | Formal, mostly written |
| Verb, た-form | 引き受けた + 上は | 引き受けた上は | Formal, mostly written |
| する verb | 決心した + 上は | 決心した上は | Formal, mostly written |
Use the dictionary form for an action that is about to happen. Use the た-form for an action that is already done. With nouns and adjectives, 以上 is usually used instead: 学生である以上.