1. 连词的定义
连词就是连接句子或句子元素的词。句子的元素有三种，词汇，短语，独立句。(conjunction来自于拉丁语，由拉丁语con和jungere连接组成。)
短语(phrases)：指由相关的单词组成的句子的元素。
独立句(proposition)：由主谓相结合的独立成份或独立表达句，或简单说成主谓独立句。
(1) Hamilton AND Jefferson were distinguished statesmen.
连词“and”将词汇“Hamilton”与“Jefferson”连接起来作为动词“were”的主语的主体部分。
(2) The sound of failing waters OR of the resulting leaves is agreeable to the ear.
连词“or”将两个短语“of failing waters”和“of the resulting leaves”连接起来作为名词“sound”的修饰语。
(3) [James will come ] IF [you call].
连接“if”将两个独立句“James will come”和“you call”连接起来，前一个句子是主独立句，第二个句子是子独立句，或从句(clause)。
2. 连词的分类
按照其用途，连词可分为两类：并列连词(co-ordinate)， 主从连词(subordinate)。
2.1 并列连词
并列连词用于连接以下成分：(a) 在句子中相对于其它单词具有相同的文法功能功的词汇和短语；(b) 位于同一层级的独立句，即连接的两个独立句同为互相独立，或同为相互依赖。
(1) The winds AND the waves are absent there.
“winds”和“waves”具有相同的关系——相对于动词“are”来说，都作为主语，因此，从结构上讲，and是并列连词。
(2) The boy is always running down to the river OR into the woods.
短语“to the river”和“into the woods”对于动词“is running”而言具有相同的关系(作为副词短语修饰动词)，因此，or是并列连词。
(3) [He chid their wanderings] BUT [relieved their pain].
用but连接的两个独立句具有相同的层级——每一个都是独立的表达句，因此，but是并列连词。
主要的并列连词有：
and，neither，either，whether，but，nor，or，both.
相关性连词(correlatives)：一些并列连词是成对的使用，即并列连词具有相互关系，称为相关性连词。
Both—and……It is both yours and mine.
Either—or……He is either a knave or a fool.
Neither—nor……Neither the horse nor the carriage was injured.
Whether—or……It matters little whether I go or stay.
2.2 主从连词
主从连词用于将一个主独立句与一个从独立句连接起来。主从连词从来都不仅连接词汇。
If we cannot remove pain，we may alleviate it. (如果我们不能根除疼痛，或许我们可以缓解它。)
I fled because I was afraid. (我因害怕而逃走。)
主要的主从连词有：
that，though，for，if，although，till，lest(唯恐，以免)，after，until，unless，before，because，notwithstanding(尽管，虽然)，since，except.
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选出下列句子中的连词并将其归类：
1. Take heed lest ye fall.
2. I have cut my finger, therefore I cannot write.
3. I fear I shall fail, but I shall make the attempt.
4. I shall make the attempt, though I fear that I shall fail．
5. He speaks so low that he cannot be heard.
6. Remain where you are till I return.
7. He will neither come nor send an apology.
8. It ls as cold as Iceland.
9. I know not whether to go or to remain.
10. Ask James if he is ready; and if he is ready, tell him to follow as quickly as he can.
11. He did not deserve to succeed; for he made no effort, and showed no Interest.
12 I shall not go unless you call me, nor will I remain if I can avoid It.
13. I can wonder at nothing more than how a man can be idle; but of all others a scholar.
14. The precise era of the invention and application of gunpowder is involved In doubtful traditions and equivocal language; yet we may clearly discern that it was known before the middle of the fourteenth century；and that before the end of the same the use of artillery in battles and sieges, by sea and laud, was familiar to the states of Germany, Italy, Spain, France, and England.
15. Whether he was combined With those of Norway; or did line the rebel With hidden help and vantage; or that with both He labor'd in his country’s wrack, I know not.
3. 感叹词(interjection)
感叹词是描述一种情绪或情感的词，但是它并不进入句子的结构，不能算作句子结构的一部分：例如，Oh! Ah! Alas! Hurrah!
注意：关于感叹词的深入讨论将会在句法章节展开。
来源：<<英语文法和写作>> William Swinton，1879 年版。
