Please read the blog post naturally. It is available at https://dictionaryblog.cambridge.org/2017/08/09/ill-believe-it-when-i-see-it-talking-about-certainty-probability-and-possibility/. You may feel it easier to read the post there. Thank you!
I’ll believe it when I see it: talking about certainty, probability and possibility
By Liz Walter on August 9, 2017
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.
