其實(shí),這四個(gè)單詞除了詞性不同,中文意思差不多,用法在一定程度上可以互換,我把各個(gè)詞語用的最多的意思例舉出來.
assure vt 保證,擔(dān)保； 使確信；向.保證（重點(diǎn)使用）； 弄清楚
He hastened to assure me that there was nothing traumatic to report.
他急忙向我保證沒有任何不快的事要報(bào)告.
sure adj 確信的,必定的（重點(diǎn)使用,用作adj）； 可靠的 adv 當(dāng)然,的確
He'd never been in a class before and he was not even sure that he should have been teaching.
他以前從未講過課,他甚至不能確定自己是否應(yīng)當(dāng)從事教學(xué).
The president has never been sure which direction he wanted to go in on this issue.
這位總統(tǒng)從未確定在這個(gè)問題上自己想要朝哪個(gè)方向走.
ensure vt 保證,確保（重點(diǎn)使用）；使安全
We must ensure that all patients have access to high quality care.
我們必須確保所有的病人都能夠得到高質(zhì)量的護(hù)理.
insure
vt 確保,保證,給.保險(xiǎn)（重點(diǎn)使用）
vi 確保,投保
For protection against unforeseen emergencies,you insure your house,your furnishings and your car.
為防止發(fā)生無法預(yù)料的緊急情況,人們給房屋、家具和汽車投保.
All the electronics in the world cannot insure people against accidents,though.
不過,世界上所有的電子設(shè)備并不能保證意外的發(fā)生.