I’ll believe it when I see it: talking about certainty, probability and possibility

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by Liz Walter

Benjamin Franklin famously wrote that ‘nothing can be said to be certain, except death and taxes’. We all know how annoying it can be when someone seems to be completely sure about all their opinions, so it is important to be able to express certainty only where it is justified, and other degrees of probability or possibility where they are appropriate.

The most common way to do this is to use modal verbs. Compare the following sentences:

School pupils will do better with this new teaching method.

School pupils may/might/could do better with this new teaching method.

The second sentence shows that something is possible, not certain. Another way of softening the first sentence would be to start it with a phrase such as In my view, In my opinion, or (more informally) I think (that). This would show that you realise that other people might not agree.

We also use modal verbs to speculate about things, i.e. to say what we think is true. The verbs we use for this depend on how certain we are. We use must and can’t for things we are quite sure about because we have some evidence:

She’s been in the sea for hours – she must be very cold.

He can’t have forgotten – I reminded him this morning.

We use may, might and could for speculating on things we are less sure about:

They may have decided to get a later train.

She might not know that she needs a visa.

Of course, there are many other ways of expressing degrees of certainty. The most basic is simply to use adjectives such as possible, probable, (un)likely and certain or adverbs such as possibly, probably, definitely and certainly:

A broken wire was the probable cause of the fire.

We definitely won’t finish this work today.

These phrases are used when we are fairly sure about something:

In all probability, they will lose their jobs.

It’s a fair/safe bet that Tom will discover our secret.

The chances are we’ll have moved house by then.

To show that we are less certain, but still think that something is possible, we could say:

I’m not sure he’ll win, but anything’s possible.

 She could become president. Stranger things have happened.

And finally, if you are sure that something will not happen, you can say:

If he pays you back, I’ll eat my hat.

 Adam’s going to tidy his room? I’ll believe it when I see it!

For more information about modal verbs, see my post from last November.

20 thoughts on “I’ll believe it when I see it: talking about certainty, probability and possibility

  1. Hadeel Hammam

    If my stubborn daughter changes her mind and she agrees to marry you, even though stranger things have happened, I will eat my hat, but notice that, my dear, I haven’t one…

  2. As English language was my favourite subject at school when I was young but now I am old I still have interest in exercisin my brain so it may not become dormant. I don’t mind having more knowledge from the vocabularies which are very important in speech making. Thanks.

    1. Rosa Melissa

      It’s my wish, too.
      I’d like to train my English just because I wouldn’t forget it.
      But I don’t know I can.

  3. Daniel Melton

    You forgot the Oxford commas. Yes, it is something that should always be used when listing items; not using them can change the intended meaning. Probability and possibility cannot be combined, therefore, an Oxford commas is needed: “Certainty, probability[,] and possibility.”
    The subjects studied in my paralegal class had its own week respectively: criminal, civil, and wills and trusts, to name a few.
    Wills and trusts are combined in the same week, therefore, no comma needed to separate.
    Thyme, basil, salt, and pepper. (All in individual containers.)
    Thyme, basil, and salt and pepper. (Salt and pepper mixed in a single container; same as cinnamon and sugar mixed.)
    When looking at a restaurant menu, it is so irritating to see a list of ingredients in a meal description of individual owns that is without that comma!

    1. Liz Walter

      Hi Daniel – personally I’m a fan of the Oxford comma, but most people aren’t, and so I tend not to use it unless there’s a genuine danger of ambiguity, which I don’t think there is in ‘certainty, probability and possibility’. In fact, schoolchildren in the UK (as part of their year 6 SATs tests) are explicitly taught *not* to use it. However, I can see that in a legal document, the Oxford comma could be extremely important!

  4. Tiffany

    I’m a nurse I’ve met alot of people of different organs that speaks different dialects I’ve been trying to learn how to speak Spanish for awhile now can someone help me or guide me into the right direction so that I can begin the process of learning Spanish

  5. Akbar Safi

    In ‘definitely’ and ‘probable’ there is 100% certainty?
    And in ‘In all probability’, ‘It’s a fair/safe bet’ and ‘The chances are’ also bear 100% certainty or just more than 75%?

    Please I’m not quite sure about this blog, if you, briefly, write them in percentages, it would be a great help to me.
    Thank you Madam!

    1. Liz Walter

      definite is 100%, probable is more than 50% – remember that if you’re not sure about words, you can look them up in the very good online dictionary on this site.

  6. Olga Martinez

    Thank you for a useful explanation, Liz! What about the expression “be bound to”? Could it also be included in this lesson?

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