unreal actions in the past

If +s+ V(present simple), S+V(present simple)

If + present simple, will + Vinf

If S+ V(past perfect) ..., S+ could/would +have+VpII

If S+V(past simple)..., S+would/could+V(in)+O

if you heat ice,it melts

if you heat ice,it melts

If i were you,i would go out for lunch

Ex: If I had seen you then, I would have invited you to dinner.

Real or likely situations in the present or future and their results

If you take the pills, you will feel better

unreal actions in the present