Duty 和 responsibility 都意為「責任、職責」，是兩個相當常用的字，但含意略有不同，不能視為完全同義詞。譬如說，在 I will take responsibility for bringing the kid home. (我會負責帶小孩回家) 這句中，responsibility 不可用 duty 來替代，因為 take responsibility for 為固定用語。
Duty 意為「責任、職責；義務」，是指依照道德和法律的標準和規定，一個人永遠要盡的義務，強調自覺性，如 It is our duty to defend our country. (保衛國家是我們的義務)；Most women have a strong sense of family duty. (大多數女性都有強烈的家庭責任感)；Everyone has a duty to his country. (每個人對其國家都有應盡的義務)；Her duties include typing documents and making coffee. (她的職責包括文件打字和煮咖啡)。
Responsibility 意為「責任、職責」，是指任何義務、職責、責任或職務上所應盡的本分，強調對他人的責任，如 It is your responsibility to protect your children. (你有責任保護你的小孩)；It is one of the responsibilities of the government workers. (這是政府工作人員的職責之一)；You should take up your responsibility. (你應負起你的責任)；A terrorist organization has claimed responsibility for the car bombing. (一個恐怖組織宣稱該起汽車爆炸案是他們幹的)。
另外，duty 有個意思是 responsibility 所沒有的，那就是「關稅」，可用作可數或不可數名詞；這個意思也值得學習，如 Customs duties are paid on imported goods. (進口貨物要付關稅)。