[文法Q&A] if 與 whether 的用法區別 + whether 可以帶出兩種以上的可能性或選項嗎 (whether A, B, or C)?
if 與 whether 這兩個字都有表示”是否”的意思，都是連接詞，一般是可以互換使用。但是，還是有一些區別和限制。if 一般是用於口語中表示”是否”，而 whether 適用於較於正式的文體中。還有 whether 也可以置於不定詞之前，而 if 卻不行。另外，由 whether 所引導的子句可以作為介詞片語，而且也可以 whether 引導主語、同位語的子句，對 if 來說就沒有這樣的用法。 我們可以從以下例句來辨析：
1) 做為動詞受詞，或是在某些具有 「疑惑」， 「疑問」，或「不確定」意味的子句，我們可以使用 whether 子句，也可以使用if子句。whether 和 if 一般是可以互換使用。
-No one knows if the government will pass the bill (or not). (O)
-No one knows whether the government will pass the bill (or not). (O)
2) whether 可用於句首，所引導的子句當主詞，但 if 不行；If 放句首會被認為是作條件或假設。
-Whether the government will enforce the policy is something that everyone is discussing. (O)
-If the government will enforce the policy is something that everyone is discussing. (×)
3) whether 置於不定詞之前
-The students debate whether to accept the government’s offer.
4) whether 當介詞片語用
-The students are worried about whether they will be prosecuted for occupying the legislature.
5) whether 所引導的句子是屬於同位語
-The question whether there is life on Mars has been discussed for decades.
“Whether there is life on Mars” is an apposition to “question.”
However, the use of “the question of whether…” to introduce an indirect question appears to be more common.
the question whether: https://bit.ly/34SUU4d
the question of whether: https://bit.ly/3N2nql1
6) whether可以引導出兩種以上的可能性或選項嗎?
whether來自於古英語的 “hwæðer, hweðer” 表示 “which of two.”
<http://www.etymonline.com/index.php?term=whether>
大多數當代字典提到 whether 可用以引導出兩種或多種的可能性或選項, 但只提供兩選項的例句 ><:
Oxford: Expressing a doubt or choice between alternatives: he seemed undecided whether to go or stay <http://www.oxforddictionaries.com/definition/english/whether?q=whether>
Merriam Webster: alternative conditions or possibilities: see me no more, whether he be dead or no <http://www.merriam-webster.com/dictionary/whether>
Cambridge: (used to introduce two or more possibilities) it is not important if: Let’s face it – you’re going to be late whether you go by bus or train. <http://dictionary.cambridge.org/dictionary/british/whether?q=whether>
Collins: (subordinating) used to introduce an indirect question or a clause after a verb expressing or implying doubt or choice in order to indicate two or more alternatives, the second or last of which is introduced by or or or whether: he doesn’t know whether she’s in Britain or whether she’s gone to France <http://www.collinsdictionary.com/dictionary/english/whether >
Dictionary.com: used to introduce the first of two or more alternatives, and sometimes repeated before the second or later alternative, usually with the correlative or: It matters little whether we go or stay. Whether we go or whether we stay, the result is the same.
<http://dictionary.reference.com/browse/whether>
Wordsmith.net: used to introduce two or more choices or alternatives: Whether we swim or run, we will get plenty of exercise.
<http://www.wordsmyth.net/?level=3&ent=whether>
所以結論是一般的用法是只帶出兩種的可能性或選項，這也是沒有爭議的用法 。但看到帶出三種的可能性時不需驚訝，因為一些學術文章及考試也常用 whether 引導出兩種以上的選項 (e.g. whether they be A, B, or C).
e.g.
-…whether they are atoms, ants in a colony, or neurons firing in a human brain…
Frontiers of Complexity: The Search for Order in a Chaotic World
R Highfield – 1996
-…whether they be social workers, educators, public health officials, policemen, city planners, highway engineers or physicians.
Dilemmas in a general theory of planning
HWJ Rittel, MM Webber – Policy sciences, 1973 – Springer
-…whether they be growth factors, adhesion molecules or…
Cancer: An attractive force in metastasis
LA Liotta – Nature, 2001
-Shipwrecks are more likely to be found undisturbed at great depths than in shallow coastal waters, which exposes archaeological remains to turbulence and makes them accessible to anyone in scuba gear, whether they be archaeologist, treasure hunter, or sport diver.
GMAT Prep 1 no. 55.
More examples: http://scholar.google.com/scholar?q=%22whether+they+be%22&btnG&hl=zh-TW&as_sdt=0%2C5
注1：or not 通常是多餘的以上兩句，皆可省略。然而，當 ”whether or not” 意義是 “regardless of other” (不管其他/如何), “or not” 不該省略。如： The parade will go ahead whether it rains or not 遊行將繼續前進，不管會不會下雨。
而 The New York Times Manual of Style and Usage 是認定 whether 字句當主詞，受詞，或介詞片語時，or not可省略。然而，當 whether 字句是副詞時 or not 不該省略 (The parade will go ahead [v. phr.] whether it rains or not [adv.]).
<http://www.pearsonlongman.com/ae/azar/grammar_ex/message_board/archive/articles/00095.htm>
注2：or not 可以放在 whether 後或子句後。然而，or not 不能直接放置 if 後。
English explanation: http://www.quickanddirtytips.com/education/grammar/if-versus-whether
Image source: http://tinyurl.com/kzfpgn7
Sources:
http://www.eng.fju.edu.tw/etc/quiz/common%20files/I.htm
http://siro.moe.edu.tw/fip/index.php?n=5&m=0&cmd=content&p=504&o=2
http://www.quickanddirtytips.com/education/grammar/if-versus-whether?page=all
http://www.wordsmyth.net/?level=3&ent=whether
http://dictionary.reference.com/browse/whether
http://www.collinsdictionary.com/dictionary/english/whether >
http://dictionary.cambridge.org/dictionary/british/whether?q=whether>
http://www.oxforddictionaries.com/definition/english/whether?q=whether
http://www.etymonline.com/index.php?term=whether
http://www.pearsonlongman.com/ae/azar/grammar_ex/message_board/archive/articles/00095.htm