if

• “如果”是最常见的条件连词，用来引导条件从句，表示主句所述情况发生或成立所依赖的条件；也用于谈论可能性、假设情形、真实条件及其后果，还可表示“是否”。

If is a very common subordinating conjunction used to introduce conditional clauses. It expresses a condition that must be met for the situation in the main clause to happen or be true. It is essential for talking about possibilities, hypothetical situations, real conditions, and consequences.

1. Real / Possible ConditionA2formal

   Used to talk about real or possible situations in the present or future. The if-clause describes a realistic condition, and the main clause shows the likely result. This is the most common use of "if" (first conditional and zero conditional).

   真实 / 可能条件

   • If it rains tomorrow, we will stay at home.
   • If you study hard, you will pass the exam.
   • If you heat water to 100°C, it boils.
   • Call me if you need any help.
   • If she arrives early, we can start the meeting on time.

2. Hypothetical / Unreal ConditionB1formal

   Used for imaginary or unlikely situations in the present or future, or for situations that are contrary to past facts. The if-clause describes something that is not real or not very probable, and the main clause shows the hypothetical result (second and third conditionals).

   假设/非真实条件

   • If I were rich, I would travel around the world.
   • If she knew the answer, she would tell us.
   • If I had studied harder, I would have passed the test.
   • What would you do if you won the lottery?
   • If he hadn't missed the train, he would be here now.

3. Polite Requests and Indirect QuestionsB1formal

   If is often used in polite requests, offers, and indirect questions instead of more direct forms. It softens the sentence and makes it sound more courteous.

   礼貌请求与间接问句

   • If you could help me, I would really appreciate it.
   • If you don't mind, could you open the window?
   • I wonder if you have seen my keys.
   • If possible, please send the report by Friday.
   • Let me know if you can come to the party.