Modal Deduction

Modal Verbs Use:

We use Modal verbs to express: Abilities, Requests, Advice, Offers, Deductions, Commands, and Probabilities in the future. The same modal verb can have different meanings: i.e. 
Can I borrow your CD?  Request         
I can speak Spanish well!  Ability
These verbs are often called  modal auxiliary verbs, because they don’t need an auxiliary to form a negative or interrogative phrase.
ex: I Can’t speak Spanish well. not  I do not can speak Spanish well.
Modal verbs can be can be formed in the past, present or future: the forms may change accordingly.
Note Important! Modal verbs never go with to and no  s  in the third person.
In this section we are going to look at the modal verbs that are used to make deductions about a situation in the present past or future. We use different modal verbs  according to our degree of certainty.

 

Must

Might

May

Could

Can't

 

Affirmative form

Long formsContracted forms
You might be ill.  We think something is possible but not sure.not possible
You had better catch the bus.
He/she must be in Spain. We feel sure or realistic possibility.

Negative form

 
Long formsContracted forms

I should not play football.     

I shouldn’t play football.
You had  better not catch the bus.You‘d better not catch the bus.
He/she/it ought not go out. This form is not usually used in the  negative form!He/she/it oughtn’t go out.
 

Interrogative form

 
Long formsContracted forms
Should I play football?        not possible
Had you better catch the bus?     
Ought he/she/it go out. This form is not usually used in the  interrogative form!