Grammar Notes: Unless & if … not
Original examples (not copied from any textbook).
1. If … not
Use if + subject + don’t / doesn’t + verb to say the action might not happen, then give the negative result with won’t or will not.
Example: If the agency doesn’t extend night buses, many workers won’t get home easily.
2. Unless
Unless means “except if” or “if … not.” Put the condition after unless in the present; put the consequence in the other clause.
Example: Many workers won’t get home easily unless the agency extends night buses.
3. Avoid double negatives
Do not combine unless with not in the same condition (e.g. avoid unless you don’t).