Now that you're studying English at a 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.

Whether 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 certainty of going IF they had more money, which they don't.

So the certain prediction exists, but in an imaginary or unreal situation.

The modal "might" expresses 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.