Zero type: If + present simple + present simple
If + present simple + imperative
(for natural events, for general truths)
Type I: If + present tenses + will, shall, can, must, should, may…
Type II: If + past simple + would, should, could, might…
(for unreal conditions)
Type III: If + past perfect + word have verb3
Mix type: If + past perfect + would, should, could…
(for regret and complaint now)
- After if clause any modal verb cannot be added into the sentence.
- Neither parts of the if clause can include modal verbs.