Not if, but when…

If and when

If whenThe expression ‘not if, but when’ is a helpful way to remember the main difference between if and when in the context of talking about the future. This phrase is used to express that something –  either positive or negative – will definitely happen in the future. This something, the when, is more significant to the speaker than the if part of the sentence.

Here are some common situations in which you might use this phrase:

Use it when you believe something is not just a possibility (if I get the job…), but an eventuality (when I get the job…). Often, it’s used along with ‘it’s (not) a matter of’ or ‘it’s (not) a question of’.


  • Not if I run a marathon, but when!

It can also be used like this:

  • It’s a matter of when I get the job, not if!

And here’s an example with a more negative tone:

  • It’s not a question of if, but when the next cyber attack will strike.

Grammar point – if and when for the future

If is used to express a possibility in the future, whereas when is used for things that will happen. 


  • When I go out later, I’ll pick up some groceries. (certain to happen)
  • If I go out later, I’ll pick up some groceries.  (might happen)


(if clause) (main clause)
If + subject + simple present + rest of clause, subject + will + bare infinitive + rest of clause.
If I go out later, I’ll get some groceries.

If the main clause is first, there is no comma.


  • I’ll pick up some groceries when I go out later.