Now that you're studying English at high level,let's get a better understanding of modals.
By now you should already have a good understanding of what they mean.
Here are the modals which are used to express degrees of certainty.
Will Shall May Can
These modals are used for making predictions,judgements and speculations.
They indicate how much a speaker knows about the likelihood of an event.
First,the modal "will" expresses certainty,as in "if you heat water,it will boil".
Based on what is known,the speaker is certain it will happen.
The modal "may" expresses possibility,as in"it may rain this evening,but I'm not sure".
Based on what is known,the speaker asserts that the event is possible rather than certain or impossible.
The modal "can" expresses potentiality,or ability,as in "He can afford it,but he may decide not to buy".
The modal "shall" is a bit different from the others.
"Tina shall be there" means the speaker is determined that Tina will be there.
In other words ,the speaker is determined to get her to come and will try to influence events to make it happen.
We would never say:"It shall rain".
Nobody can make it rain,so whether or not it rains is beyond anyone's control.
If someone were to say that,it would seem as if they were claiming the power to control or influence nature.
Note that the question "shall I open the door?" Invites the person who is asked to make the decision.
Wheter or not the door is opened depends on the person's answer.
In contrast,"will I open the door?" asks for a prediction rather than a decision.
Note that these modals can be weakened or removed from reality by the use of their past tense form.
Would Should Might Could
"We would go if we had more money,but we don't."
This sentence expresses the speaker's certaninty of going IF they had more money,which they don't.
So the certain prediction exists,but in imaginary or unreal situation.
The modal "might" expresess less possibility than "may" ,so "might go" is less likely than "may go".
The modal "could" expresses less potential than "can",and is often used in conditionals.
"If he could come" expresses less potential than "if he can come."
The sentence,"if he could come,we would all be happier" expresses the feeling that in fact,he can't come.
Here is the second set of modals.
These modals express degrees of logical force or social expectation.
Must Had better Should Ought to
Note that none of them has a past tense or weakened form.
The first one,"much" indicates logical or social necessity.
It expresses the strongest logical or social face.
The modals "should" and "ought to" assert that something is probable or expected,but not necessary.
The modal "had better" expresses advisability.
In other words,if someone "had better" do something,they should do it or there may be negative consequences.
Therefore,"had better" has the feeling of a threat,as in "You had better be there."
This isn't the same as "You should do it." which means you are expected to do it,but without an implied threat if you don't.
One interesting rule is that no more than one modal can be used with any verb.
There aren no expection to this rule.
Therefore,it's incorrect to say "He will must be there."
To avoid breaking this rule,there are other words taht have the same meaning,but are not modals.
In the case of "must",for example,we use "have to" as in "He will have to be there".
Similary,we cannot say "He may can come".
Instead,we say "He may be able to come."
One last thing to note about modals.
They use the same form regardless of what the subject is.
If the grammatical subject is I,it,we or they,we use the same form,will.
We would never say"He wills be there."
But with non-modal forms,such as "have to" we must change the form to match the subject.
"He has to be there" and "I have to be there".
Repeat
The modal "will" shows that the speaker is making a predication with certainty.
She has something else planned for that evening,so she can't come to the party.
It isn't certain,but there's a good probability that they will finish at five.
We don't know for sure,but there is still a possibility that they can leave on Friday.
"What must we do?" has the same meaning as "What do we have to do?"
Tom must be taller than Sue because he's taller than Ben and Ben is taller than Sue.
The expression "be able to" has the same meaning as "can".but isn't a modal.
