助動詞與語氣助動詞
Helping and Modal Auxiliary Verbs

　

助動詞

助動詞 (helping verbs or auxiliary verbs) -- 如 will, shall, may, might, can, could, must, ought to, should, would, used to, need -- 與主動詞 (main verbs) 連用來表達時間和語氣的狀態。助動詞與主動詞結合起來就產生所謂的動詞片語或動詞字串 (verb phrases or verb strings)。在下面的句子中，"will have been" 是助動詞，而 "studying"是主動詞；整個動詞字串以加底線來表示：

  • As of next August, I will have been studying chemistry for ten years.

學生應該記住副詞和縮短字並非動詞的一部份。在 "He has already started." 這個句子中，副詞 already 修飾動詞，但它並非動詞的一部份。"He hasn't started yet." 中的   n't 也是一樣 ( 以縮短的 n't 來表示的副詞 not 並非動詞 has started 的一部份)。

Shall, will 以及 have, do 和 be 的各個型態與主動詞結合來表示時間及語氣的狀態態。做助動詞時，be, have 和 do 會隨著主詞和時間的變化而改變型態。

  • I shall go now.
  • He had won the election.
  • They did write that novel together.
  • I am going now.
  • He was winning the election.
  • They have been writing that novel for a long time.
在美國，除了第一人稱的禮貌問句 (表請示之意) 外，很少使用 shall：
  • "Shall we go now?"
  • "Shall I call a doctor for you?"

(在第二句中，許多寫作者會使用 should 來取代之。) 在其他所有情況中，都是使用 will 來表示未來式。這種幾近完全排除以 shall 來表示未來式的作法，在英國英語中比較沒有那麼絕對。

語氣助動詞

其他助動詞稱為語氣助動詞 (modal auxiliaries or modals)，如 can, could, may, might, must, ought to, shall, should, will 和 would 。它們不會隨不同的主詞而改變型態。在下列不同主詞的句子中，你不妨拿這些語氣助動詞一個一個地來置換 can，看看情況會怎麼樣。

I
you (單數)
he
we
you (複數)
they		 can write well.

接下來我們將討論四個最常見且在應用上比較容易出問題的語氣助動詞。之後，我們將以列表方式再探討語氣助動詞所表達的能力、可能性、勸告、必要性、請求和許可等不同的意思，並輔以不同時態的例句。

Can 和 Could，May 和 Might

might 和 may 是比較麻煩的語氣助動詞的其中兩個。當用於表示許可或請示的句子時，might 是 may 的假設法過去式。might 比 may 客氣很多，含有比較沒把握，猶豫的意思。

  • May I leave class early?
  • If I've finished all my work and I'm really quiet, might I leave early?

在表示可能性的句子中，may 和 might 是可以互換的現在式及未來式型態，而 might + have + 過去分詞是過去式：

  • She might be my advisor next semester.
  • She may be my advisor next semester.
  • She might have advised me not to take biology.

語氣助動詞 can 被用來

  • 表示能力 (有能力做某事或知道如何做某事的意思)：
    He can speak Spanish but he can't write it very well.
  • 表示允許 (被許可或允許做某事的意思)：
    Can I talk to my friends in the library waiting room? (注意：can 沒有 may 那麼正式；此外，若干寫作者反對在這種句子中使用 can。)
  • 表示理論上的可能性：
    American automobile makers can make better cars if they think there's a profit in it.

語氣助動詞 could 被用來

  • 表示過去的能力：
    I could always beat you at tennis when we were kids.
  • 表示過去或未來的許可：
    Could I bury my cat in your back yard?
  • 表示現在的可能性：
    We could always spend the afternoon just sitting around talking.
  • 表示有條件的可能性或能力：
    If he studied harder, he could pass this course.

在表示能力時，can 和 could 通常也含有願意的意思：Can you help me with my homework?

語氣助動詞的意思與時態

BE ABLE TO 現在式或未來式 過去式
能力 Juanita is somehow able to attend school and be a great mother for her four children. Josie was never able to meet her boss's expectations.
CAN 現在式或未來式 過去式
許可 Can I go to the movies? [沒有 "may" 來得正式；若干人士反對這種句子中使用 "can"。] He could have gone to the movies, but he didn't ask.
能力 I can do my algebra homework by myself. Last year, I couldn't do my algebra without a tutor's help.
禮貌的請求 Can you help me after class? [沒有 "will"，"could" 或 "would you mind"  來得正式。] 沒有過去式
可能性 The New England Blizzard can win a lot of games this season. 沒有過去式
COULD 現在式或未來式 過去式
許可 Could I please leave now? He could have left now, but he didn't ask to be excused.
可能性 It could be a great year for the New England Blizzard. It could have been a great year if it weren't for all those injuries.
禮貌的請求 Could you change my tire for me? [比 "can" 或 "will" 更正式。] 沒有過去式
HAD BETTER 現在式或未來式 過去式
勸告 You had better quit smoking now. You should have quit smoking last year. [表示遺憾]
HAVE TO 現在式或未來式 過去式
必要性 She has to pay her tuition before she can attend classes. She had to pay her tuition before she could attend classes.
MAY 現在式或未來式 過去式
許可 May I go to the movies? 沒有過去式
可能性 It may be a good year for the New York Giants. It may have been a good day for her, but I'm not sure.
猜測 It's June already; my father may plant his garden this weekend. It's June already so my father may have planted his garden last weekend.
MIGHT 現在式或未來式 過去式
可能性 It seems rather unlikely, but the Bulls might win another championship.[表達可能性較 "can"，"may" 或 "could" 來得小的事。] It seemed unlikely, but the Bulls might have won another championship.
MUST 現在式或未來式 過去式
必要性 You must pay your lab fees before entering the laboratory. (must：必須) 沒有過去式。過去式常使用 "had to" 來代替：He had to pay lab fees before entering the laboratory.
推斷 Your wife's been gone a week. You must miss her. [表示一項近乎確定。] (must：一定) You look exhausted. You must have been up all night. [表示對過去某事的確定。]
猜測 It's noon so she must be on her way home. (must：應該) 沒有過去式
NOT HAVE TO 現在式或未來式 過去式
無必要性 During Amnesty Week, you don't have to pay library fines. It was Amnesty Week, and he didn't have to pay library fines.
NOT NEED TO 現在式或未來式 過去式
無必要性 If you take the Charter Oak Bridge, you don't need to pay tolls. Before they paved this highway, you didn't need to watch out for traffic.
OUGHT TO 現在式或未來式 過去式
勸告 You really ought to quite smoking now. He really ought to have quit smoking. [大多數寫作者都比較喜歡使用 "should have quit"。]
期望 The bus ought to arrive by eight o'clock. The bus should have arrived by eight o'clock. [表示失望的期望；巴士應該在八點之前來，但還沒來。]
SHOULD 現在式或未來式 過去式
勸告 You really should quit smoking now. He should have quit smoking earlier. [表示遺憾。]
期望 The bus should be here before eight o'clock. The bus should have been here by eight o'clock. [巴士被預期會抵達，但它尚未抵達。]
猜測 It's noon so she should be home soon. 沒有過去式
WILL 現在式或未來式 過去式
禮貌的請求 Will you help me with my homework? [比 "can" 較正式一點，但比 "could" 較不正式一點。] 沒有過去式
WOULD YOU MIND 現在式或未來式 過去式
許可 Would you mind if I brought my brother to your wedding? Would you have minded if I had taken my brother to your wedding.
禮貌的請求 Would you mind helping me with my homework?  沒有過去式

Guide to Grammar and Writing