1、However, but, yet, while, whereas 表轉折的區別
表示轉折關系的並列連詞
- however: 然而，不過。位置句首、句中，用逗號隔開；語氣比but 弱，不直接引出相反意見。用作副詞較常見。
I’d like to go with you, however, my hands are full.
He said that it was so; he was mistaken, however.
He apologized to me. However, I didn’t forgive him.
- but: 但是，用來引出相反意見或不同情況，常用於口語中。連接兩個並列的成分或句子，語氣較強，在意義上構成明顯的對比。與前分句可用（可不用）逗號，與后分句不用逗號。
I’d asked everyone but only two people came.
It is cold in summer here, but it is not cold in winter.
It was a sunny but not very warm day.
She wanted to go swimming, but her parents told her not to.
I ought to have helped her, but I never could. 我本該幫她但沒能。
Honey is sweet, but the bee stings. 蜂蜜很甜，但蜜蜂有刺蜇人。
- yet: 作連詞時，“然而，可是，卻，而”，與but相比，比較的意味較強，經常以and yet形式出現。
It’s a small car, yet it’s surprisingly spacious.
It’s freezing cold. Yet you have to go out, don’t you?
I don’t like him, and yet I have to work with him.
He said he was our friend, yet he wouldn’t help us.
- while: 並列連詞時，while conj. 然而 = whereas 表示對比或用於引出相反的情況。只強調兩者之間的對比，並不強調轉折。並列句、且兩個句子謂語動詞同時發生或結構相同。
You like playing tennis, while I like reading.
I earn only 80 dollars a week, while she earns 100 dollars.
Some men are rich while others are poor.
Jane is slender while Mary is stout. 簡苗條而瑪麗強壯。
Motion is absolute while stagnation is relative. 運動是絕對的，而靜止是相對的。
There’s plenty of rain in the southeast, while there's little in the northeast.東南部雨量充足,而西北部則很少下雨。
Some people waste food while others haven't enough.有些人浪費糧食,然而有些人卻吃不飽。
- 注1：but 一般不可與 yet, however, nevertheless 等連接性狀語連用，但可以和on the contrary, on the other hand, still 等連用。
She tried again and again, but still, she didn’t succeed. 他一遍又一遍地嘗試，但仍然沒成功。
- 注2：表示轉折概念的詞：
still, yet, however, nevertheless, on the other hand, on the contrary, conversely, all the same, though, after all, for all that, in the meantime等詞語。這些詞在本書中都作為連接性狀語處理。
- 注3：一句話區別：
but 口語常用詞，語氣較強，泛指與前述情況相反，放句中。
however 表轉折關系，語氣稍弱於but，連接性也弱一些，因而常作插入語，放句中，常常在前面用逗號。
still 語氣強，多用於肯定句或疑問句。指盡管作出讓步，采取措施或表示反對，但情況仍然如故，無所改變。
yet 常用於否定句，語氣比still稍強。指不管作出多大努力或讓步，仍達不到預期的結果。一般放在句末,前面一般不用加逗號。
nevertheless 指盡管作出完全讓步，也不會發生任何影響。
while 表對比，一般可與whereas換用，但程度弱一些。
whereas 表對比，一般可與while互換。
- 注4：only 用作表示意義轉折的並列連詞，只見於非正式文體。
You may go, only come back early. (only =but) 你可以走，但要早點回來。
He wants to buy the watch, only he can’t afford it. 他想買這塊表，但他買不起。
- 注5：however 釋義
adv. 無論如何；不管怎樣 However hard it may be, do your best.
adv. 盡管如此；然而 Later, however, he decided to go.
adv. (表示驚奇)怎樣；怎么 However did you find it? 你是怎樣找到它的？
conj. 不管怎樣；不管用什么方法 He can go however be like.他想怎么去都行。
2、whereas與while的區別
1.whereas = while
while前后句子之結構要求並列相對，whereas 在結構上則不一定不需要嚴格平行。（OG12-131）
whereas/while這種連詞連接的比較成分不要求含義上絕對的平行
2.whereas連接的平行比較只要求對比的核心邏輯上有對稱關系，不要求對稱位置必須是對稱名詞，下面句子中主從句的主語分別是energy和nuclear power並不是對稱名詞，但是對比的核心都是“核能發電占總產出能量的份額”，如OG12-131:
Over 75 percent of the energy produced in France derives from nuclear power, whereas nuclear power accounts for just over 33 percent of the energy produced in Germany.
*：
- 但是如果whereas后面接介詞短語，那么主句的開頭也必須需要是介詞短語(whereas后出現介詞短語或者狀語都會非常對稱)如OG-113：
Whereas in mammals the tiny tubes that convey nutrients to bone cells are arrayed in parallel lines, in birds the tubes form a random pattern.
- 如果whereas后接單純主謂賓（或主系表），主句也要盡量用單純的主謂賓（或主系表）來對應，如prep08 194:
Whereas the honeybee’s stinger is heavily barbed and cannot be retracted from the skin, the yellow jacket’s stinger is comparatively smooth, and can therefore be pulled out and used again.
3.while 引導的從句:
1)意思是“當…時”，放句首或句中
2)意思是“轉折對比contrast”時，多放在句中，也可以放在句首。while表示對比概念的時候，兩個事物要是同時發生（但是while本身並沒有at the same time的意思，所以while at the same time是可以prep 1-96）。
3)意思是“雖然、盡管”（讓步）時，多放在句首。(=although)
4)表示條件,意為"只要",其意思和用法相當於as long as。while可位於句首,也可位於句中。
*：While放在句中時要特別注意，像OG12-131的A選項，ETS說while 放在中間表示“同時發生”的意思大於對比的意思。
Over 75 percent of the energy produced in France derives from nuclear power, while in Germany it is just over 33 percent.
2.1、更多例子：
從屬連詞whereas意為：“然而，但是，反之”（but, in constrast, on the contrary, while）用於陳述相反的話，引出表示對比、對立或直接相反（Direct Opposition）的狀語從句，是正式用法，語氣強並且書卷氣較重，通常多位於居中，也可置於句首；通常多用逗號隔開，也有語法學家和某些權威詞典主張不用逗號。如
（3）His parents were rich, whereas mine had to struggle.
（4）Many small birds use new sites for each nesting, whereas large birds often reuse the same nest.
（5）Whereas it is day with us, it is night with the Americans. (=It is day with us, whereas it is night with the Americans.)
應該注意的是whereas引導的從句與主句在意義上不僅是對立和相反的，而且也是並列的（因此也有人認為whereas是並列連詞），兩者可以互換，無論主句在前，還是從句在前，其句意都不變。如
（6）Old people in my country usually live with their children, whereas the old in the United States often live by themselves. (=Whereas old people in my country usually live with their children, the ole in the United States.)
即使主句和從句改變詞序，其實際意義也大體相同。如：
（7）They want a house, whereas we would rather live in a flat. (=Whereas we want a flat, they would rather live in a house.)
那么，whereas 與while可以換用嗎？兩者有何區別呢？
同樣，while也可意為：“（然）而，但是，反之”（but, whereas）,也可引出表示對比或相反情況的狀語從句，相當於whereas，兩者通常可以換用，但不如whereas正式，語氣也不如whereas強,是普通用語，更為多用。如：
（8）They spend all their money on their house, whereas(while) are prefer to spend ours on traveling.
（9）While(Whereas) some newspapers have no advertising at all others carry many advertisements.
與whereas一樣，主句和從句之間通常也用逗號隔開，但也可不用。如
（10）That region has plenty of natural resources while this one has none.
同樣，也有人將while看作並列連詞。順便說一下，whilst 與while 同義，但比while正式，尤其多用在英國英語中，如：
（11）Raspberries have a matt, spongy surface whilst blackberries have a taut, shiny skin.
最后，where作連詞用時，也可意為：“（然）而，反之”（but, whereas）,引出表示對比或與主句意思相反的狀語從句，相當於意思接近於whereas和while，但通常多用於口語，而whereas是正式用法，多用於書面語（但有時也可用於口語）。如句（７）中的whereas可換用where而意思不變。又如：
（12）Some people spend their spare time reading, where others watch television.
（13）She is very diligent, whereas(while, where) he is very lazy.
值得注意的是whereas和while也可引出讓步狀語從句（adverbial clause of concession, 意為：“雖然，盡管”（although）,多位於句首，比較文氣。如：
（14）Whereas the amendment is enthusiastically supported by a large majority in the Senate, its fate is doubtful in the House.
（15）While I admit that there are problems, I don’t agree that they cannot be solved.你的問題或可得到解決。
參考：
http://blog.sina.com.cn/s/blog_149f8478a0102x16g.html
https://forum.chasedream.com/forum.php?mod=viewthread&tid=770110&page=1&fid=23&showoldetails=yes
http://blog.sina.com.cn/s/blog_4c100dc80100vvrz.html