What are modals of speculation?Modals of speculation are modal auxiliary verbs which express degrees of certainty. In other words, they describe a fact or situation that is definite, probable, possible, or impossible from the speaker's point of view. (As the speaker is speculating, he/she may be wrong.) Here we'll focus on speculating about present or future events.

For example:I may buy a new computer this summer, if I can afford it. He might go back to school for his Master's Degree next year, but he hasn't decided yet.

What is the sentence structure?

The sentence structure is as follows:    subject  |  modal verb  |  (negation)  |  main verb  |  object/complement

    He  |  must  |  (not)  |  be  |  very happy.    Sandy  |  may  |  (not)  |  study  |  abroad next fall.

The main verb is always in the plain form, even when the sentence expresses the future.

How are modals of speculation used?

Commonly used modals for present and

future events include the following:

Must / will express a definite situation, and

must not / will not / could not an impossible

one. 

On the other hand, may / may not / might /

might not / could aren't as clear. 

The conversation and intonation may subtly

change the meaning. 

However, may /may not are more certain

than might / might not / could, and these last

three modals express a weak probability.

must:    + He must really enjoy life because he always has a smile on his face.    - He must not (mustn't) be very happy if he always has a frown.will:    + If all countries stop polluting, greenhouse gases will significantly drop.    - Many industrialized countries will not (won't) stop polluting the environment!may:    + Sandy may study abroad next fall, but only if she gets good grades this spring.    - If Sandy doesn't get good grades this spring, she may not study abroad next fall.might:    + Although we might have cars that fly in 50 years, I doubt it.    - Gasoline-powered transportation might not exist in 50 years. We'll use electric cars.could:    + I could vote for in the next election if one of the candidates interests me.    - Jim is very conservative. He could not (couldn't) ever vote for a liberal politician.