however，whereas，while，yet 这组词都含 “而、然而、却” 等转折的意思。

however：“然而、可是” 语气较弱, 联接也较少松弛. 因此常被用来插人句子中间。

You ask me to do the work; I am afraid_ however_ that I amnot equal to it. “你请我做这事，然而，我恐怕不能胜任。”

whereas ：“而、却、反之、其实” 表示较为鲜明的对比或对照，语气强烈，也较正式。

After the exhausting journey, he fell ill , whereas I was only alittle tired. “令人疲惫的旅行结束后他病倒了，而我只不过稍觉疲倦罢了。”

while：“而、却、虽然” 表示对比，但语气较弱。 While the doctors did all they could, they couldn't save her life;the next day after the operation，she died. “虽然医生已尽其所能，但仍未救活她的命，手术第二天她就死了。”

yet：“而、然而、可是”，正式用语，让步转折的语气较强烈，而且多指付出了努力，却与预期结果或主观打算相违背。常用短语：and yet 然而、可是：but yet 但是还…

可还是.… His speech was almost unintellgible , ( and ) yet for some unknown reason I enjoyed it very much. “他的演讲虽有些莫名其妙，但不知为何我却非常愿意 (喜欢) 听。”