5. Modals Of Deduction And Speculation

Modals of deduction and speculation:

This is a great topic, here you will learn what the modals of deduction and speculation are and then we will look at using them in a practical way.

Modal verbs

The modals of deduction and speculation are used when we want to make a guess about something and we choose the verb depending on how sure you are.

The two main forms: 

1. Deducing and speculating about present 

2. Deducing and speculating about past 

Deducing and speculating about present

Structure: [Subject + modal verb + infinitive] 

He might arrive.

We should go.   

*Remember: Modal verbs normally don’t use the preposition “to” (“ought to” is the exception)


The use of will and won’t is used in condition when you are very sure. 

Example: She will be at office now 


Must is used when you are sure something is true, or it’s the only realistic possibility.

Example: You don’t have a jacket. You must be freezing!


Might is used when you are not sure about something, but there is a possibility of that happening. Let’s say that there is a 50/50 chance. 

Example: There is still time, he might make it to the party.


It is used very similarly to might, to express that something is possible, but you’re not sure. It is also used to express permission to do something. 

Example: You may come in. 

Example: This may take a long time. 


The use of should and shouldn’t is used when we are making an assumption about what is probably true. 

Example: He should arrive there soon. 

Note: Should is primarily used for recommendations and suggestions, but in this topic we’re focusing on deduction and speculation.


The use of can takes place when generally something is possible

Example: The cost of cars can be very high here. 

Deducing and speculating about past 

We use the following structure to speculate about past events: 

[Modal + have + past participle]

Like in the present, the modal verb we use tells us how sure we are, or about our speculative thoughts.

They must have missed the plane! (I’m quite sure they missed the plane)

We might have passed the exam. (I think we have passed the exam, but I’m not sure)

You could have been more honest. (Being more honest was a possibility)

Casey should have arrived an hour ago! (He planned to arrive an hour ago, but he’s not here.

Likely and unlikely

Likely and unlikely are adjectives. If something is likely to happen it means that it will probably happen or that it is expected to happen. If something is unlikely to happen it means that it probably won’t happen. We can use these two adjectives in two ways:

It is likely/unlikely that + clause

It’s likely that in just a few years we will change our economic model.

It’s unlikely that the police had anything to do about it. 

Subject + be likely/unlikely + to + infinitive

He is likely to win this game. 

They are unlikely to reach an agreement. 


To form this structure easily, consider it to be similar to “going to”, and we simply replace the word going.

I am going to travel to China – 100%

I am likely to travel to China – 55-80%

I am unlikely to travel to China – 1-40%