正確に理解しておいてほしい文法事項の一つが Conditionals です。さぁーと読み飛ばしてしまいがちですが、自分が正確に理解していたかどうかを確かめてみましょう。
まず、簡単に言ってしまうと、conditionals は、大きく2つに分けることができます。一つは、real conditionals で、もう一つは、unreal conditionals です。前者は、起こりえることを仮定した文、後者は、事実とは異なること、あるいは、起こりそうもないことを仮定した文になります。それぞれ、下記の例文で確かめてみましょう。
1 Real conditionals
a Real present conditionals
If it rains, we carry our umbrellas.
Water boils if it is heated to 100 degrees Centigrade.
In the real present condition. A present tense is used in the if-clause and a present tense is used in the result clause (the main clause). In these examples, the simple present is used. However, depending on the intended meaning, the present progressive, a present modal, or the present perfect could also be used, as the following examples.
If it is raining, we may carry our umbrellas.
Water boils if it has been heated to 100 degrees Centigrade.
b Real future conditionals
If it rains tomorrow, we will carry our umbrellas.
In a real future condition, we use present tense (any present tense) in the if-clause, and a future tense (any future tense) in the result clause (the main clause).
If the sun is shining tomorrow, he will have already gone to the beach by the time we get into his house.
* The modal “will” is never used in an if-clause.
2 Unreal conditionals
a Unreal present/future conditionals
If you studied harder, I’m sure you would do better in school.
If I called the president, he probably wouldn’t speak to me.
The verb in the if-clause is identical in form to the past and the verb form in the result clause (the main clause) begins with the modal would / could / might plus the simple form of the main verb. In reality, either the simple past or the past progressive could all be used in the if-clause.
If the children were playing instead of sleeping, their mother might be very angry.
* Progressive forms are possible in the result clause (the main clause).
If their mother were working now, the children would probably be playing.
b Unreal past conditionals
If there had been more time, we would have finished the project. (But, in reality, we didn’t have more time, and we didn’t finish the project.)
My sister would never have seen South America if she hadn’t met that young man from Bolivia. (But she did meet that man from Bolivia, so she has seen South America.)
In the unreal past, the verv in the if-clause is identical in form to the past perfect (or past perfect progressive) and the verb in the result clause (the main clause) contains the modal would / could/ might plus the perfect auxiliary have plus the past participle of the main verb.
If she hadn’t been dancing, she would never have broken her leg.
If we had seen you at the party, we might have stayed longer.
* As with the unreal present, the result clause (the main clause) may contain a progressive form.
If I had taken that job with so little money, I would have been watching every penny I spent.
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