How to Express Uncertainty in English

Usually, when we say something in English, we’re making either a positive sentence:

“My cat likes eating cake.”

or a negative sentence:

“My cat doesn’t like it when I play guitar.”

For both these sentences, we’re 100% sure about these facts:

100% sure it’s true		100% sure it isn’t true
“My cat likes …”	⇿	”My cat doesn’t like …”

But what if you aren’t sure?

What if you need to express something in the middle?

That’s when you need to express uncertainty in English.

How to express uncertainty in English

There are four main ways we can express uncertainty in English:

Phrases like “I think …”
Adverbs like “probably”
Modal verbs
Phrases like “Don’t quote me on that”

Let’s look at them one by one.

Expressing uncertainty in English with short phrases

Just by adding a short phrase like “I think” or “I reckon” to the beginning of your sentences, you can add a feeling of uncertainty.

So you can have sentences like:

“I think your cat smells.”

“I reckon we’re only going to be a few minutes late.”

The structure is really simple.

Use the phrase first, then add “that” (if you like), then start your sentence:

phrase	“(that)”	sentence
I think	(that)	your cat smells.

Here is a list of these kinds of phrases in order of strength:

Very certain
- I’m sure … “I’m sure he likes you! Don’t worry!”
- It’s probable … “It’s probable that we’re going to get a big bonus this year!”
- I’m pretty sure … “I’m pretty sure that you’re not supposed to push that button!”

Quite certain:
- I think … “I think we should do that again!”
- I don’t think … “I don’t think he knows what he’s talking about.”
- I reckon … “I reckon you need another cup of coffee.”
- I believe … “I believe they told us they’d be here at eight.”

Uncertain:
- It’s possible … “It’s possible that they forgot to leave the WiFi password.”
- There’s a chance … “There’s a chance that we’ll miss the flight if we don’t leave now.”
- I imagine … “I imagine it’d be easy to get into the party.”
- I suppose … “I suppose there’s a long queue for that one. It’s really popular.”
- I guess … “I guess he didn’t think about your feelings.”

Expressing uncertainty in English with adverbs

You can use adverbs to express different levels of uncertainty.

What the adverbs mean

Almost definitely | Almost certainly

As you can probably guess, when you use these phrases, you’re saying that you’re really, really, really sure something happened. You’re just not 100% sure.

Probably

When we say something probably happened, we’re saying that we’re pretty sure it happened.

It’s basically a little less certain than “almost definitely.”

Apparently

This one’s a little different.

When we use “apparently,” it’s like we’re saying, “I don’t know for sure, but someone told me this.”

It’s like you’re not taking responsibility for the statement and instead you’re putting the responsibility onto whoever said it in the first place.

Pretty useful, right? With one word you can say, “If this isn’t true, it’s not my fault!”

Possibly

“Possibly” is pretty uncertain. When you use this word, you’re really saying that you’re not sure at all.

How to use these adverbs in a sentence

Most of the time, put these adverbs just before the main verb.

That means that if you have an auxiliary verb (like “has”), then the adverb goes after it:

“She’s probably been swimming.”

And if you don’t have an auxiliary verb (like with the present simple and past simple tenses), then you just have the adverb after the subject:

“The bank manager almost certainly ran away with all the money.”

Here they are for each tense:

Simple tenses:

subj.	adverb	verb	object
My cat	probably	escaped	through the window.
My cat	definitely	doesn’t know	what she’s doing.

Other tenses:

subj.	aux verb	adverb	verb
My cat	is	almost certainly	sleeping	right now.
My cat	will	definitely	be	really annoying.
My cat	has	probably	left	the building.

When the sentence is negative, however, we usually put the adverb BEFORE the auxiliary:

subj.	adverb	aux verb	verb
My cat	almost certainly	isn’t	sleeping	right now.
My cat	definitely	won’t	be	reading a book.
My cat	probably	hasn’t	eaten	your sushi.

You can also put these at the end, but if you do, they often sound less certain, as if they were an afterthought:

“My cat won’t be really annoying, possibly.”

“Of course it’s legal, probably.”

Also look out for “apparently.” “Apparently” only feels comfortable when you put it at the end or the beginning (not in the middle).

“The ice cream delivery was cancelled, apparently.”

“Apparently, you’re the best they’ve ever seen!”

Expressing uncertainty in English with modal verbs

Modal verbs are a simple, elegant and useful way of expressing uncertainty in English.

They look great, too!

You can use them to express uncertainty about the past:

“Sheila can’t have gone to the shops. Look! Her shoes are still here!”

About the present:

“We must be flying over Belgrade. Check out the rivers!”

And about the future:

“We might be able to finally leave after another hour of waiting.”

When you’re expressing uncertainty in English with modal verbs, you might want to ask yourself two questions:

How certain am I?
When am I talking about?

Let’s look at the first question:

How certain am I?

Remember this table?

100% sure it’s true		100% sure it isn’t true
“My cat likes …”	⇿	”My cat doesn’t like …”

As you can see, you can be very sure something DIDN’T happen (on the right of the table).

You can be very sure that something DID happen (on the left of the table).

And you might be somewhere in the middle.

Here’s how we express these with modals:

“I’m sure this didn’t happen”	“Maybe this didn’t happen.”	“Maybe this happened.”	“I’m sure this happened.”
couldn’t	might not may not	might may could	must

Want some examples?

In a minute.

But first, we need to know when we’re talking about.

When am I talking about?

So we know what level of certainty the modal verbs express.

But we need to ask when we’re talking about.

Is it the past, present, future, general?

Let’s look at how to do that.

tense	modal form	examples
past	modal + “have” + verb3	“Carol’s not here. She must’ve taken the dog out for a walk” “Your dad couldn’t have met Houdini. He’s not old enough!”
present	modal + “be” + verb-ing	“Sales can’t be going down! We’ve spent so much on advertising!” “We might be living in the weirdest period of history ever!”
future	modal + verb1	“I don’t know. We might not make enough money to stay open next year.” “He’s saying that AI might take over the world and make us slaves.”
general time	modal + verb1	“You run 30 km before work? You must get up very early!” “Look at his hair! He can’t be over 50 years old!”

Adding other forms

It’s also quite common to add other forms to these modals, especially “going to,” “have to” and “used to.”

“It was after eleven, so they can’t have been going to meet Andy. He starts at ten.”

“Surely they must have to stop smoking when they join the monastery, right?”

“Judging by how tired you look, I’m guessing you might not have got used to life on the farm yet.”

Bringing it together

So, we’ve looked at the two main questions:

How certain am I?
When am I talking about?

Now, let’s bring it together into one mega-table!

	very sure (negative)			very sure (positive)
past	“She couldn’t have come here all the way from Ankara.”	“Danny might not have had enough time to pick up some wine.”	“OK. I might not have locked the front door. Do you want me to check again?”	“It must’ve rained! Look at the puddles!”
present	“That guy can’t be getting nearer. He’s not walking or anything.”	“I think the rain might not be dying down for a while.”	“You never know! She could be walking here right now!”	“That doesn’t smell good! The pizza must be burning! Turn the oven off!”
future	“They can’t be starting in an hour! Nothing’s ready!”	“I think we might not have to work on Friday!”	“He’s saying that AI might take over the world and make us slaves.”	“Danny must be taking the 9:45 to Norwich.”
general time	“It can’t be that easy!”	“The shop might not be open on Sundays.”	“It might only work when it isn’t raining.”	“The sea must be just behind those buildings.”

Notice that we usually use continuous forms when we’re very sure about the future.

“They can’t be starting in an hour! Nothing’s ready!”

“Danny must be taking the 9:45 to Norwich.”

Expressing uncertainty in English with phrases like “Don’t quote me on that”

You can also express uncertainty in English with full clauses or sentences.

These sentences are like a “disclaimer” to whatever you’re saying.

It’s like a way of softening your statement so it feels like you’re not pushing too hard.

This is especially useful in delicate situations like business negotiations, discussion about politics or talking to some difficult relatives over a big family dinner.

All these phrases have the same function, and you can use them interchangeably.

Here they are: