1、主语： (1)由名词、代词(人称代词用主格)、动词不定式、动名词等充当,说明动作是“谁”发出的，
1、主语：
(1)由名词、代词(人称代词用主格)、动词不定式、动名词等充当,说明动作是“谁”发出的，主语是句子陈述的对象，说明是谁或什么，表示句子说的是“什么人”，或”什么事“，如“我写字”中的“我”，做出写字这个动作。“写”则是谓语，“字”是宾语，是接受谓语“写”这个动作的对象，因此是宾语。如：The painter painted a very nice picture. (画家画了一幅漂亮的画。) / They fought against SARS bravely. (他们勇敢地与非典搏斗。) / To see is to believe. (耳听为虚眼见为实). / Helping animals is to help people. (帮助动物就是帮助人类。)
(2)动词不定式或动名词做主语时可用it代替,而不定式或动名词移至表语或宾语之后。如：It is very comfortable to have a Class A seat during the long journey. (在长途旅行中能有个甲等座位简直太舒服了。) / Eating too much is bad for your health.(=It is bad for your health eating too much.) (吃得太多对你的身体不利。)（比较好看，避免头重脚轻）
(3)口语中常见主语或“主--系”省略：(It is) nothing. ((那)没有什么。)/ (It) doesn’t matter. ((那)没有关系。) / (I) thank you. ((我)谢谢你。)
(4)反意问句的附加问句,主语必须是代词：The man looks worried, doesn’t he? (这个人看上去很着急不是吗？) / Tigers are dangerous animals, aren’t they? (老虎是危险的动物不是吗？)
(5)祈使句一般省略主语。加主语时往往用来指定某个人。Keep the keyboards clean, children. (孩子们请保持键盘的清洁。) (省略了主语) / You go there and fetch me a glass of water. (你去给我弄一杯水来。)
(6)主语一般在句首,但在问句中会处于第二位和句尾；倒装句及there be句型主语在动词之后。如：Computers are made in this factory. (计算机生产于这家工厂。) / Where are they? (他们在哪儿？) / Does the boy like staying home? (这个男孩喜欢呆在家里吗？)
(7)主语与谓语必须保持单、复数的一致, 而谓语与表语或宾语之间没有这一要求。Neither Jim nor Rose has passed the exam. (Jim和Rose都没有通过考试。) / The Chinese people are a hardworking and brave people. (中华民族是一个勤劳勇敢的民族。)
(8)主语可以由从句充当,详见“主语从句”。