Modal Verbs : speculation - may, might, must , can't

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.

+ 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.

+ If the US signs the Kyoto Protocol, greenhouse gases will significantly drop.
- Many industrialized countries will not (won't) stop polluting the environment!

+ 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.

+ 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.

+ I could vote for in the next election if one of the candidates interests me.
- Jim just loves President Bush. He could not (couldn't) ever vote for a Democrat.

Is there additional information on modals of speculation?
There are a few more important points to consider. First, modal verbs never take a third-person singular s, as in: If it snows this afternoon, Tim coulds be late. In addition, modal verbs are always followed by a verb in the plain or bare infinitive form, never to + verb. So the following sentence is wrong: Time could to be late. Lastly, the contraction of might not is mightn't. However, this is rarely used nowadays and should generally be avoided.

What are modals of speculation?
Modal auxiliary verbs express degrees of certainty. In other words, they describe a fact or situation that is definite, probable, possible, or impossible. However, despite the degree of certainty (or uncertainty), the speaker may be wrong. Here we'll focus on speculating about past events. For example:

A: Kelly must have gone somewhere tropical for vacation, because she's sunburned.
B: Actually, I she got some free tickets for a tanning salon. She didn't go anywhere last week.

What is the sentence structure?
The sentence structure is as follows:

subject | modal verb | (negation) | have | past participle | object/complement

Mary | must | (not) | have | done | well on the test.
Jennifer | could | (not) | have | made | as much money as she claims.

How are modals of speculation used?
Commonly used modals for past events include the following:

Must have expresses a definite situation, and must not have /could not have an impossible one. When we use may have /may not have, we aren't as certain. And when expressing weak probability, use might have /might not have /could have.

+ She must have gone somewhere tropical for vacation, because she's sunburned.
- She must not (mustn't) have enjoyed her weekend skiing, because she broke her leg!

+ Alex may have spent some time in Paris because he often talks about the city.
- Alex may not have enjoyed Paris, because he rarely says anything positive about the city.

+ The economy might have gotten worse without the tax cuts.
- The tech bubble might not have happened if people had invested more carefully.

+ Kerry could have won the 2004 election if he had responded to the attacks on his character.
- Gore could not (couldn't) have won the 2000 Presidential election.

Is there additional information on modals of speculation?
Yes, there is. When speculating about past events, the sentence must use have + past participle, such as: have seen / have done / have gone. However, the phrase or sentence which provides the reason need not be restricted to the present perfect tense. Kelly must have gone somewhere tropical for vacation, because she's sunburned. = She's sunburned now, which has made people think she went on vacation.