Usando os Verbos Modais para falar sobre probabilidade no passado e presente

1: Talking about the present:

must / might / could / may / can't

• must + infinitive
• might / might not + infinitive
• could / could not + infinitive
• may / may not + infinitive
• can't + infinitive

For example:

I am waiting for Julie with another friend, David.
I ask: 'Where is Julie?'
David guesses:

• She must be on the bus. (I'm fairly sure this is a good guess)
• She might come soon. (maybe)
• She could be lost. (maybe)
• She may be in the wrong room. (maybe)
• She can't be at home. (I'm fairly sure this isn't true)

Notice that the opposite of 'must' is 'can't in this case.

Will / won't

We use will and won't when we are very sure:

• She'll be at work now.

Should / shouldn't

Should and shouldn't are used to make an assumption about what is probably true, if everything is as we expect:

• They should be there by now.
• It shouldn't take long to drive here.

This use of should isn't usually used for negative events. Instead, it's a better idea to use will:

• The underground will be very busy now (not: 'should be').

Can

Can is used for something that is generally possible, something we know sometimes happens:

• Prices can be high in London.

Can is not used to talk about specific possibilities:

• He could be on the bus (not: 'can be').

2: Using modal verbs to talk about the past:

must / might / could / may / can't + have + past participle

(Click here to review how to make the past participle)

• must have + past participle
• might / might not have + past participle
• could / couldn't have + past participle
• may / may not have + past participle
• can't have + past participle

For example:

You: Where was Julie last night?
David:

• She must have forgotten about our date.
• She might have worked late.
• She could have taken the wrong bus.
• She may have felt ill.
• She can't have stayed at home.

Will / won't + have + past participle

Will and won't / will not + have + past participle are used for past certainty (compare with present use of 'will' above):

• The parcel will have arrived before now.

Should + have + past participle

Should + have + past participle can be used to make an assumption about something that has probably happened, if everything is as we expect (compare with present use of 'should' above):

• The train should have left by now

Could

We can use could + infinitive to talk about a general possibility in the past (compare with the use of 'can' above):

• Prices could be high in the sixteenth century.

This is not used to talk about specific possibilites in the past (instead we use could + have + past participle):

• He could have been working late (not: 'could be'. As this is a specific possiblity, 'could be' is present tense)

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Vídeo: It must have  been love - Roxette

Letra e Tradução:

http://www.vagalume.com.br/roxette/it-must-have-been-love-traducao.html

Exercícios:

http://www.perfect-english-grammar.com/modal-verbs-of-probability-exercise-1.html

http://www.perfect-english-grammar.com/modal-verbs-of-probability-exercise-2.html

http://web2.uvcs.uvic.ca/elc/studyzone/410/grammar/410-modals-of-possibility-and-probability-for-past-situations1.htm

http://web2.uvcs.uvic.ca/elc/studyzone/410/grammar/410-modals-of-possibility-and-probability-for-past-situations2.htm