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needing to be done; requiring a response
当為とは義務のことだ。
Sollen refers to what ought to be done.
問題を解決するのは当為だと感じた。
Felt that resolving the problem was something that had to be done.
哲学では当為は事実から導き出せないとされている。
In philosophy, what ought to be is said to be underivable from what is.