一）If +动词原形，...+动词原形.表达现在的真实情况或习惯

1）If I shop online ,I save time.

2)  If  the mall is closed,you can shop online.

二）If +动词原形..,..will/might/be going to +动词原形..表达将来或预期的真实情况

1）If we study hard,we will/might speak English very well.

2) If you fell lucky,you're going to expect good things.

三）If+过去时,  would(not)+动词原形...对现在的虚拟表达现在或将来的不真实存在

1）If he had more money now,he would take a trip around the world.(事实上他没有去旅游）

2）If I had a chance to change my life,I would become a younger lady.

3). If she were* rich ,she would live Shanghai .（事实上她没有住在上海）

4)  If I were you ,I would have a meal outside.(多用于提换位思考性建议）

** wish +过去式，表达想要，但不是真实的

       1)I wish I were a fish .

        2)I wish I could speak English very well.

四）If had +过去分词...，would have +过去分词。表达对过去的虚拟（有时表的对过去的后悔等）

1）If I had won a million dollars,I would have  traveled around the world，

       （我没有贏100万）

2）If I had studied English hard,I would have been able to communicate with                             

       foreigners.

3)  if I had been free ,I would have gone to the movies with you.

    （后悔没去看电影）

   **wish +had + 过去分词也表达后悔

    I wish I had  visited the famous museum!