If you ascertain the truth about something, you find out what it is, especially by making a deliberate effort to do so.
例句
Through doing this, the teacher will be able to ascertain the extent to which the child understands what he is reading...這樣一來，老師就能確定孩子們對他所讀的內容理解多少了。Once they had ascertained that he was not a spy, they agreed to release him...一旦確認他并非間諜，他們即同意將他釋放。
英英詞典釋義
Adjective
1. discovered or determined by scientific observation;
"variation in the ascertained flux depends on a number of factors""the discovered behavior norms""discovered differences in achievement""no explanation for the observed phenomena"