Modal auxiliary verbs are mainly used to convey the mood of speaker. To express certain degree of likelihood or certainty, modal verbs like may, might, could, and must are used. Let’s see the degree of certainty expressed by these modal verbs.
Degree of certainty
Generally, there are two types of auxiliaries used to express certainty of events. Modal verbs are used to describe likelihood in percentage; whereas, verbs + be are preferred for complete sense of certainty .
For complete likelihood, verbs + be- is/are/will…. are preferred.
Here, there is no chance for doubt. These are used for complete sense.
Certainty in percentage
•Near certain — Must,
•Half certain — may,
•Weak certain — might, could,
•Rarely used for present and past certainty — will/would.
Certainty means the degree of likeliness about something occur or happen in immediate present, near future.
“Must” modal auxiliary is used for near certainty. It means that when the chance of an event or situation are more to happen, must modal auxiliary is preferred.
•I think you must be free on Sunday. Would you help me to learn swimming, please? (but, only when he has no other assignments)
•In the first week of June, it must be hot and humid. (but, it depends on the other elements of atmosphere)
•He has just recovered from the phase of depression. Hope, he must have been feeling better now.
•Wow, this is so beautiful lake ! I think, it must be pollution free for now.
Certainty by may
It is commonly used modal verb for possibility. But, the level of certainty it expresses is not more than half.
•It looks like that it may be our biggest mistake.
•As time passes, cyclone may loose strength.
•Once I get selected, it may prove my best achievement.
•I don’t think solar energy may prove a viable alternative for conventional energy as of now.
•She is so out spoken. One day, she could find herself in trouble.
•He is a risky trader. Very soon, he could loose all his capital.
•We have enough time, we might reach there on time.
•Now, the program might begin any time.
Apart from these modal verbs, will and would are also used to express certainty of present and past in certain situations.