導語：公共英語的寫作不僅要積累相關的寫作模板，還要具備一定的寫作語法，下面YJBYS小編分享2017下半年公共英語5級寫作語法指導，歡迎參考!
1.概念
虛擬語氣用來表示說話人的主觀願望或假想，所說的是一個條件，不一定是事實，或與事實相反。
2.在條件句中的應用
條件句可分為兩類，一類為真實條件句，一類為非真實條件句。非真實條件句表示的是假設的或實際可能性不大的情況，故採用虛擬語氣。
真實條件句
真實條件句用於陳述語氣，假設的情況可能發生，其中if是“如果”的意思。
時態關係
句型：條件從句+主句 一般現在時：shall/will + 動詞原形
If he comes, he will bring his violin.
典型例題
The volleyball match will be put off if it ___.
A. will rain B. rains C. rained D. is rained
答案B。真實條件句主句為將來時，從句用一般現在時。
注意：
1) 在真實條件句中，主句不能用be going to表示將來，該用shall, will.
(錯) If you leave now, you are never going to regret it.
(對) If you leave now, you will never regret it.
2) 表示真理時，主句謂語動詞便不用shall (will) +動詞原形，而直接用一般現在時的動詞形式。
非真實條件句時態：可以表示過去，現在和將來的情況。它的基本特點是時態退後。
a.同現在事實相反的假設。
句型：條件從句+主句
一般過去時：should(would)+動詞原形
If they were here, they would help you.
b.表示於過去事實相反的假設。
句型：條件從句+主句
過去完成時：should(would)have+ 過去分詞
If she had worked harder, she would have succeeded.
The rice would not have been burnt if you had been more careful.
If my lawyer had been here last Saturday, he would have prevented me from going.
If he had come yesterday, I should / would have told him about it.
含義：He did not come yesterday, so I did not tell him about it.
If he had not been ill and missed many classes, he would have made greater progress.
含義： He was ill and missed many lessons, so he did not make greater progress.
c.表示對將來的假想
句型：條件從句+主句
一般過去時：should+動詞原形/were+不定式/would+動詞原形/should+ 動詞原形
If you succeeded, everything would be all right.
If you should succeed, everything would be all right.
If you were to succeed, everything would be all right.
混合條件句主句與從句的動作發生在不同的時間，這時主，從句謂語動詞的虛擬語氣形式因時間不同而不同，這叫做混合條件句。
If you had asked him yesterday, you would know what to do now.
(從句與過去事實相反，主句與現在事實相反。)
If it had rained last night (過去), it would be very cold today (現在).
虛擬條件句的倒裝
虛擬條件句的從句部分如果含有were、should、或had可將if省略，再把were、should或had移到從句句首，實行倒裝。
Were they here now, they could help us.
=If they were here now, they could help us. Had you come earlier, you would have met him
=If you had come earlier, you would have met him.
Should it rain, the crops would be saved.
=Were it to rain, the crops would be saved.
注意：
在虛擬語氣的從句中，動詞“be”的`過去時態一律用“were”，不用was，即在從句中be用were代替。
If I were you, I would go to look for him.
如果我是你，就會去找他。
If he were here, everything would be all right.
如果他在這兒，一切都會好的。
典型例題
_____ to do the work, I should do it some other day.
A. If were I B. I were C. Were I D. Was I
答案C. 在虛擬條件狀語中如果有were, should, had這三個詞，通常將if省略，主語提前, 變成 were、should、had+主語的形式。但要注意，在虛擬條件狀語從句中，省略連詞的倒裝形式的句首不能用動詞的縮略形式。如我們可說 Were I not to do，而不能說 Weren’t I to do.
besides
except
except for
except that
but
but for besides除t know Peter except that hes an Japanese.
Theres nothing but a chair in the room.
But for your help，I wouldnt have finished my homework.
注意：
(1)形容詞最高階前要用the，而副詞最高階前的the可省。
(2)下面這些詞的比較等級可在後面加-er/-est或在前面加more/most構成。
cruel， often， able， clear， clever， correct， dear， free， friendly， happy， handsome， likely， lively， pleasant， right， simple， quiet， solid
， strange， strict， stupid， wrong， etc.
5. 形容詞、副詞比較等級常用的句型及用法：
類別 用法及意義 句型結構 例句
原級 沒有比較 very / so / quite / too， etc. +原級 It was very warm yesterday.
二者比較程度相同 as+原級+as+比較物件 You are as clever as Mike.
一方是另一方的幾倍 s as+原級+as+比較物件 This bridge is five times as long as that one.
二者比，程度不同 as+原級+as+比較物件 You are not as tall as he.
二者比，前者不如後者 so+原級+as+比較物件 Math isnt so hard as physics.
比 較 級 二者比，一方比另一方更re younger than Tom.
二者比，A比Bs much hotter today than it was yesterday.
A比B甚至還要s still stronger than Jack.
Hes far older than you.
表越來越s getting fatter and fatter.
understand.
A比B(高，長s getting healthier and stronger than his brother.
表比s less rich than he.
表與其說，不如s more than a teacher.
Shes more than tired.
表並不比某某s no taller than you.
最高階 三者或三者以上比較某某最s one of the best students in this class.
第幾大/長s a letter for you.
用於指初次提到某人/物 She has a dog.
指某類物或人中的任何一個 A horse runs fast.
用在不可數名詞前表一次/場/或一個/種人或物 I would like a coffee.
用於時間、度量衡名詞前表每一 He has two meals a day.
用於某些習慣用語或固定片語中 as a result，have a rest
have a chat，in a hurry
have a word with sb.
a little，a lot，a pair of
a cup of，a great deal of.
