ascertain v.查明，確定 ( 由事實查明，如通過檢查或試驗 )
【例】We must ascertain the usual customs of the local people.
我們必須瞭解當地人民的風俗習慣。
【根】as朝向，certain肯定的→朝向肯定→確定

as (當做) + certain (確定) → ascertain 確定

We need to ascertain what the problem is so that we can fix it.