if的用法

(表示条件)如果 ,主句用将来时，if从句用现在时表示将来 He will come if you invite him. 如果你请他,他会来的。 2. (表示虚拟)假如,要是 1）时态：可以表示过去，现在和将来的情况。它的基本特点是时态退后。 a. 同现在事实相反的假设。 句型 ： 条件从句 主句 一般过去时 should( would) +动词原形 If they were here, they would help you. b. 表示于过去事实相反的假设。 句型： 条件从句 主句 过去完成时 should(would) have+ 过去分词 If she had worked harder, she would have succeeded. The rice would not have been burnt if you had been more careful. If my lawyer had been here last Saturday, he would have prevented me from going. If he had come yesterday, I should / would have told him about it. 含义：He did not come yesterday, so I did not tell him about it. If he had not been ill and missed many classes, he would have made greater progress. 含义： He was ill and missed many lessons, so he did not make greater progress. c. 表示对将来的假想 句型： 条件从句 主句 一般过去时 should+ 动词原形 were+ 不定式 would + 动词原形 should+ 动词原形 If you succeeded, everything would be all right. If you should succeed, everything would be all right. If you were to succeed, everything would be all right. 3. 是否 = whether 连接宾语从句 I wonder if she is ill. 不知她是否病了。

做假设用。

If首先可以是如果的意思，但还要注意在宾语从句中是是否的意思，还要注意下主将从现，希望能帮到你

如果有两种用法 一种如果 一种是否在什么情况下？一、if作为连词，引导条件状语从句，表示“如果”等。在复合句中如果主句用将 来时，则if引导的状语从句用一般现在时（最基本的）。eg.If it doesn’t rain, we will go to the picnic next Sunday. 如果天不下雨，下周日我们将去野餐。二、if还可以引导让步状语从句。在意义上相当于even if,eve...