[Grammar] Degree of certainty

[newkeenlearner]

hi ,

I have learned that "may,might,could" used for degree of certainty in present and future and past , and "will" used for degree of certainty in future.
will is 100% and other three ones are 50% or less.
So, what about "can"?

These sentences express degree of certainty:
Banning smoking will help people to avoid the risk of illness. "It is about 100% certainty"
Banning smoking may,might,could help people to avoid the risk of illness. "It is about 50% of certainty."
Banning smoking can help people to avoid the risk of illness. "I don't know about this."

 

[newkeenlearner]

You cannno apply percentages to these words.

'Will' shows absolute certainty in the mind of the speaker. The others express possibility. We have no idea how likely the situation is.

Thanks teacher.
In the grammar book that I read modal of certainty:It only introduces "will,could,might,may". for future or present certainty, and "can" is not used in this meaning.
Source: English Grammar Betty Azar.