Definition of Auxiliary Verbs: the word help the main verb making a tense 兼用助動詞︰am, is, are, was, were, have, has, had, do, does, did, need, dare, used 專用助動詞（亦稱“情態助動詞”）︰shall, should, will, would, can, could, may, might, must, ought, had better
1.兼用助動詞︰既可當助動詞又可當主動詞的動詞 am, is, are, was, were, have, has, had, do, does, did, need, dare, used 助動詞 主動詞 Lisa is reading a novel. Lisa is a student. He does not live in . He does his homework carefully. You needn’t tell her the truth. You need a new dress. We used to sing songs in KTV. We used a pen to write.
Mary may not come tomorrow. 2.專用助動詞︰只可作助動詞不可當主動詞的動詞 shall, should, will, would, can, could, may, might, must, ought, had better You should study hard. He can run very fast. Mary may not come tomorrow.
3. 助動詞的特點︰ (1) “專用助動詞”無人稱與數的變化 (2) “專用助動詞” 中僅ought後接to V，其 餘皆直接加動詞原形 I (He, Lisa, We, They) must study hard. You can run fast, and he can too. (2) “專用助動詞” 中僅ought後接to V，其 餘皆直接加動詞原形 You ought to be very careful. He will buy a gift for you.
(3)“兼用助動詞”之後有的有to，有的則無 I don’t know him. I have to leave for Taipei now. (4) need（必需/需要）/ dare（敢）在否定句及疑問句中要加省略to的不定詞 I daren’t go out alone at night. Need I get up at five a.m. tomorrow?
(5) 過去式的助動詞未必指過去的事，可能是指現在或未來，除非上下文有明顯的過去時間或談到過去的事 (5) 過去式的助動詞未必指過去的事，可能是指現在或未來，除非上下文有明顯的過去時間或談到過去的事 Could you lend me a pen? 《註》請問或拜託時，用could比較正式； 也可用can，但多用於熟人的情況，would情況亦類似
You should take care of your dog carefully. 《註》 should除作shall的過去式外，在表示主詞的責任或義務“應該” 時要用should而非shall