1)在主語從句中的應用

It is demanded / necessary / a pity + that…等結構的主語從句，謂語動詞用should 加動詞原形，should 可省略。

It is 可用的詞有三類that(should)dosuggested, ordered, required, proposed, demanded, requested, insisted等important, necessary, natural, imperative, strange等a pity, a shame, no wonder等

2)在賓語從句中的應用

在表示命令、建議、要求等一類動詞后面的從句中，像order， suggest， propose， require， demand， request， insist， command， insist + (should) do等。例如：

I suggest that we (should) hold a meeting next week. 我建議下周召開個會議。

He insisted that he (should ) be sent there.他要求被派到那兒去。

注意：如suggest， insist不表示"建議" 或"堅持要某人做某事時"，即它們用于其本意"暗示、表明"、"堅持認為"時，賓語從句用陳述語氣。

判斷改錯： (錯) You pale face suggests that you(should)be ill.

(對) Your pale face suggests that you are ill.

(錯) I insisted that you(should)be wrong.

(對) I insisted that you were wrong.

3)在表語從句，同位語從句中的應用

suggestion， proposal， idea， plan， order， advice等名詞后面的表語從句、同位語從句中要用虛擬語氣，即(should)+動詞原形。例如：

My idea is that we(should)get more people to attend the conference.我的想法是讓更多的人來參加會議。

I make a proposal that we(should)hold a meeting next week.我提了個建議，下周我們開個會。