English — unless

The linking word unless introduces a negative condition. It has the same meaning as if… not: the result happens only when the other thing does not.

How it works

✓ Rule

Unless introduces a condition that prevents or provides an exception to the stated outcome; it usually means if… not. So I won't go unless you come is the same as I won't go if you don't come. For ordinary future reference, keep the verb in the unless-clause in a present form: Unless it rains, we'll stay inside.

Examples

unless and its if… not equivalent
Sentence with unless	Same meaning with if… not	Verb after unless (present)
I won't go unless you come.	I won't go if you don't come.	come
Unless it rains, we'll stay inside.	If it doesn't rain, we'll stay inside.	rains
You'll fail unless you study.	You'll fail if you don't study.	study
She won't call unless it's urgent.	She won't call if it isn't urgent.	is
Don't open the door unless I tell you.	Don't open the door if I don't tell you.	tell
We can't start unless everyone arrives.	We can't start if not everyone arrives.	arrives

Good to know

⚠ Note

Don't use will in the unless-clause: say unless you come, not unless you will come. And don't add a second negative — unless already means if not, so I won't go unless you come is right, not unless you don't come.