ALWAYS TRUE OR INSTRUCTIONS

If + <verb in present>  + <verb in present>

• If I read in the car, I feel sick.
• If you put petrol on a fire, it burns more quickly.
• If the phone rings, answer it.

You can also use "When" or "Whenever" to start the sentence.

PREDICT LIKELY RESULTS IN THE FUTURE

If + <verb in present> + <verb in future (will)>

• If we don't hurry up, we'll miss the plane.
• If you keep listening to loud music, you'll go deaf.

SPECULATION ABOUT IMPROBABLE SITUATIONS

If + <verb in past simple> + would | could | might

• If you did more exercise, you'd be fitter.
• If people didn't drive so fast, there wouldn't be so many accidents.
• If I were you, I'd think about dieting.
• If you were on a diet, you might feel healthier.

SPECULATION ABOUT THE PAST

If + <verb in past perfect> + <would | might | could> have + past participle

• If I'd had your e-mail address, I might have sent you an e-mail
• If you'd been more careful, you might not have had the accident.