主语从句是作为动词或谓语的主体的从句。它通常由连接词如that, if, whether等引导，可以包含完整的主语、谓语和宾语。例如："Whether he will come is uncertain"（他是否会来还不确定）。主语从句在复合句中充当主要部分，有助于表达更复杂的想法。

　　<例句>

　　It's certain that prices will go up.

　　物价肯定要上涨的。

　　<语法分析>

　　主语从句可以由that引导，此外还可由连接代词或连接副词引导，关系代词what或whatever也可引导主语从句。由that引导的主语从句是用的最多的一种主语从句，有时为了强调，可以把从句放在句首，而绝大部分主语从句则借助先行主语放到句子后部去。

　　<触类旁通>

　　(1)That she hasn't phoned is odd.

　　她没有来电话很奇怪。

　　语法分析：that引导的主语从句。

　　(2)That he was chosen made a tremendous stir in his village.

　　他被选中在他村子里引起很大轰动。

　　语法分析：有时为了强调或谓语较长时，可以把从句放在句首。

　　(3)It is natural that they should have different views.

　　他们有不同观点是很自然的。

　　语法分析：it+be+形容词或名词+that从句。

　　(4)It happened that he wasn't in that day.

　　恰巧他那天不在。

　　语法分析：it+动词+that从句。

　　(5)It's doubtful whether we'll be able to come.

　　我们是否能来还是个疑问。

　　语法分析：连接代词或连接副词可引导主语从句。

　　(6)What will be,will be.

　　该发生的事，总会发生。

　　语法分析：关系代词型what也可引导主语从句。

　　<巩固练习>

　　(1)______ he is still alive is a consolation.

　　(2)It's strange ______ she knows nothing about it.

　　(3)It may be ______ you'll prove yourself the most suitable.

　　(4)______ is to be sent there hasn't been decided.

　　(5)It was clear enough ______ she meant.

　　(6)______ is over is over.

　　(7)______ he says goes.

　　(8)______ she saw made her tremble.

　　<参考答案>

　　(1)That (2)that (3)that (4)What (5)what (6)What (7)Whatever (8)What