A fellow teacher asked me a few weeks ago if I had written anything about the use of the conjunction “unless”, and if I hadn’t, would I be prepared to write something about it? Not one to refuse a challenge, I thought to myself: “Why not?”

Well, it took me longer than I thought to get round to researching this pesky grammar word and when I finally got down to working on it, I realised why I had delayed the process.

There are certain grammar rules and parts of speech that are used naturally and without thinking by native speakers all their lives until that moment when someone asks them how a certain word or expression is used and everything falls apart!
You begin to wonder whether you have grasped your native language at all. That moment came last night when I was trying to think of how I could explain the use of “unless” in a way that sounded clear to me let alone to anyone else.

I decided to give it a go and I sincerely hope that my explanation makes sense. So, here goes.


As mentioned above, unless is a conjunction which we use in conditional phrases. In written English, the clause that follows unless is the subordinate clause (SC) meaning that it needs a main clause (MC) to make a complete sentence. It is similar to how we use if in conditional phrases.

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

  • Unless it rains, we’ll go for a picnic tomorrow.
        (SC)                      (MC)

When the main clause comes first, no comma is required:

  • They won’t come unless you invite them.
         (MC)                          (SC)

Unless is like If in that we don’t use will/would after it. We only use the present simple tense.

  • Unless I hear from you, I’ll see you at 5pm.



Unless and if not

Ok, so unless is similar to “if …..not” and together they mean “except if”. Note: We refer to real conditional situations and NOT impossible situations.


  • If you don’t study, you will fail your exam./ Unless you study, you will fail.
  • We could eat at Frankie and Benny’s if they’re not closed on a Monday/ We could eat at Frankie and Benny’s unless they are closed on a Monday.
  • I’ll make dinner if nobody wants to/ I’ll make dinner unless someone else wants to.
  • If you don’t stop smoking, you will feel bad/ Unless you stop smoking, you will feel bad

that the sentence after unless is always a positive sentence. You cannot have a negative sentence after unless because that would make the sentence a double negative and senseless.

Example: Unless you don’t study, you will fail(????)

***Warning: Typical Error

We don’t use unless when we mean if.

Example: If you feel ill, I can drive/ Unless you feel ill, I can drive

Spoken English

When 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: Unless they’ve got a visitor.



Not unless
is similar to only if

  • “Shall I tell Liz what happened? Not unless she asks you (= only if she asks you)
  • Will you come shopping with me? Not unless you offer me lunch (= only if you offer me lunch)

So there you have it.
 I want to thank my fellow teacher, Tim Harrell for prompting me to write this post. I hope I was able to make sense of this rather awkward grammar point. Please let me know if there is anything else you’d like me to cover and I will do my best to research and write about it.


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Ciao for now


Cambridge Dictionaries Online
Longman Dictionary of English
English Grammar in Use (Intermediate) Raymond Murphy