when or if

Word

Explanation

Example

when

you are sure that something will happen

When I'm in Paris, I'll visit you.
(It sure, that I'm going to Paris.)

if

you are not sure that something will happen

If I'm in Paris, I'll visit you.
(It not sure, that I'm going to Paris.)

ATTENTION!
You can both use when and if when you talk about things that happen repeatedly (in generalizations).

If you freeze water, it expands.
When you freeze water, it expands.