条件句
I. If you heat ice, it melts.
II. If we catch the 10 o'clock
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条件句
I. If you heat ice, it melts.
II. If we catch the 10 o'clock
we shall (will, can, etc) get there by
lunch-time.
Ill. If we caught the 10 o'clock train, we would (could, might, etc) get there by lunch-time.
IV. If we had caught the 10 o'clock
以上四个条件句代表四种不同意义的类型。这四种类型的区别完全在于主句和分句中动词形式的相互搭配，因此在讲条件句时，首先要注意动词形式问题。
Type I
1)
例如：
If you heat ice, it melts.
If you pour oil on water, it floats.
If the temperature drops to O degrees
由上述诸例可以看出，凡表示不受时间限制的自然法则的条件句，其 if- 分句和主句的谓语动词都用一般现在时：
(If) simple present + (Main) simple
2) 表示现在习惯动作
例如：
If I make a promise, I keep it.
If you go to the movies, what kind of movie do you prefer to see?
If it rains, I go to work by car.
在上述表示现在习惯动作的条件句 中， 分句和主句的谓语动词也都是用一般现在时。
(If) simple
3) 用于表示过去的习惯动作
例如
If it rained, I went to
If I made a promise, I kept it.
If I was hungry, I usually had a full meal.
表示过去习惯动作的条件句中， if- 分句和主句的谓语动词都用一般过去时。
(If) simple past + (Main) simple past
Ill. If we caught the 10 o'clock train, we would (could, might, etc) get there by lunch-time.
IV. If we had caught the 10 o'clock
以上四个条件句代表四种不同意义的类型。这四种类型的区别完全在于主句和分句中动词形式的相互搭配，因此在讲条件句时，首先要注意动词形式问题。
Type I
1)
例如：
If you heat ice, it melts.
If you pour oil on water, it floats.
If the temperature drops to O degrees
由上述诸例可以看出，凡表示不受时间限制的自然法则的条件句，其 if- 分句和主句的谓语动词都用一般现在时：
(If) simple present + (Main) simple
2) 表示现在习惯动作
例如：
If I make a promise, I keep it.
If you go to the movies, what kind of movie do you prefer to see?
If it rains, I go to work by car.
在上述表示现在习惯动作的条件句 中， 分句和主句的谓语动词也都是用一般现在时。
(If) simple
3) 用于表示过去的习惯动作
例如
If it rained, I went to
If I made a promise, I kept it.
If I was hungry, I usually had a full meal.
表示过去习惯动作的条件句中， if- 分句和主句的谓语动词都用一般过去时。
(If) simple past + (Main) simple past