Page 266 - Practical English Usage 3ed - Michael Swan, Oxford

257
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Compare:
Ifyou eat too much, you get fat. You get fat ifyou eat too much.
For other meanings of if. see 261.10-13.
For ifand whether in indirect speech. see 276. 62l. For ifnot and uliless. see 601.
For more information about lUollldls/zould. see 633. For the difference between ifand in case. see 27l. For even if. see 189.4.
if (2): ordinary structures
Ifyou didn't study physics at school, you won't understand this book. I'll give her your love if I see her.
the same tenses as with other conjunctions
When we are not talking about 'unreal' situations (see 258), we use the same tenses with ifas with other conjunctions. Present tenses are used to refer to the present, past tenses to the past, and so on. Compare:
- Oil floats ifyou pour it on water.
Iron goes red when it gets very hot.
- IfJohn didn't come to work yesterday, he was probably ill.
As John didn't come to work yesterday, he was probably ill.
- Ifyou didn't study physics at school, you won't untkrstand this book.
Because you didn't study physics at school, you won't untkrstand this book.
present tense with future meaning
In an if-clause, we nonnally use a present tense to talk about the future. This happens after most conjunctions (see 580). Compare:
- I'll give her your love ifI see her. (NOT .•• ifI ruill see her.)
I'll give her your love when I see her. (NOT .•. whe" [ruiU see heF.)
- If we have fine weather tomorrow, I'm going to paint the windows.
As soon as we have fine weather, I'm going to paint the windows. For if+ will (e.g. if it will make you feel better). see 260.
For if+ wiU in reported speech (e.g. 1don't know ifl'll be ready). see 276.
if (3): special structures with past tenses and
would
IfI knew her name, I would tell you. What would you do ifyou lost your job?
unreal situations
We use special structures with ifwhen we are talking about unreal situations- things that will probably not happen, situations that are untrue or imaginary, and similar ideas. In these cases, we use past tenses and would to 'distance' our language from reality.
258
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if (2): ordinary structures 257
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