Unless

We use the conjunction unless to mean ‘except if’. The clause which follows unless is a subordinate clause (sc): it needs a main clause (mc) to make a complete sentence.

When unless comes before the main clause, we use a comma:

Unless[SC]it rains, [MC]we’ll go for a picnic by the river tomorrow. (We’ll go for a picnic by the river tomorrow if it doesn’t rain.)

When the main clause comes first, we don’t need a comma:

[MC]They won’t comeunless[SC]you invite them.

Unless is a conditional word (like if), so we don’t use will or would in the subordinate clause:

Unless I hear from you, I’ll see you at two o’clock.

Not: Unless I’ll hear from you …

Unless and if … not

Unless and if … not both mean ‘except if’:

We could eat at Siam Smile unless they’re closed on a Monday. (or We could eat at Siam Smileifthey’renotclosed on a Monday.)

I’ll make dinner unless somebody else wants to. (or I’ll make dinnerifnobodyelse wants to.)

Can you turn the radio off unless you’re listening to it? (or Can you turn the radio offifyou’renotlistening to it?)

We don’t use unless for things that we know to be true:

You won’t be able to get a ticket for the match unless you’re prepared to pay a lot of money for it. (The speaker doesn’t know if you’re prepared to pay a lot of money for a ticket.)

I don’t know what we would have done if we hadn’t seen you. (We did see you.)

Not: I don’t know what we would have done unless we’d seen you.

Warning:

In speaking, we use unless to introduce an extra thought or piece of information:

He didn’t even know about the crash – unless he’d heard about it on the radio.

A:
Oh look. Neil next door’s got a new car.

B:
Unlessthey’ve got a visitor.

Typical errors

We don’t use unless when we mean if:

Pete will drive if Alex can’t.

Not: Pete will drive unless Alex can’t.

We don’t use will or would in the clause after unless:

Unless you pay now, we can’t guarantee you a ticket.

Not: Unless you’ll pay now …