(1)在主语从句中用来表示惊奇、惋惜、理应如此等，其谓语形式是"should(可省) +动词原形"，常用于以下三种句型中。
句型一：It is necessary (important, natural, strange, etc) that…
句型二：It is a pity (a shame, no wonder, etc) that…
句型三：It is suggested (requested, proposed, desired, etc) that…
如：It is strange that he (should) have done that.
It is a pity that he (should) be so careless.
It is requested that we (should) be so careless.
(2)在宾语从句中用于suggest, propose, move, insist, desire, demand, request, order, command等动词后的宾语从句中，表间接的命令和建议。其谓语形式是"(should)+动词原形"。如：I suggest that we (should) go swimming.
(3)在表语从句中，表示间接的命令，要求、请求、建议、决定等，主句中的主语通常是suggestion, proposal,request, orders, idea等。从句谓语形式是"(should)+动词原形"。如：
His suggestion is that we (should) leave at once.
(4)在同位语从句中，谓语形式是"(should)+动词原形"。如：We received order that the work be done at once.
(5)在It is time that…句型中，其谓语动词形式是"动词的过去式"或"should +动词原形",should不可省。如：It's time that we went ( should )go to school.
