Uses
| Present/Future
| Past
|
1) ability;
capability
| I can run fast.
I can help you.
I am able to help you.
I will be able to help you.
| I could run fast when I was a child, but now I can't.
I was able to help you.
|
2) informal
permission
| You can use my car tomorrow.
|
|
3) polite request
| Can I borrow your pen? Could I borrow your pen?
Could you help me?
|
|
4) impossibility
(negative only)
| That can't be true!
That couldn't be true!
| That can't have been true!
That couldn't have been true!
|
5) suggestion
| — I need help in math.
You could talk to your teacher.
| You could have talked to your teacher.
|
6) less than 50% certainty
| — Where is John?
He could be at home.
| He could have been at home.
|
7) doubt; astonishment (interrogative)
| Can she know Japanese?
| Can he have done it?
|
Uses
| Present/Future
| Past
|
1) duty; obligation; strong necessity
| I must go to class today. I have to go to class today. I have got to go to class today.
| I had to go to class yesterday.
|
2) lack of necessity (negative)
| I don't have to go to class today.
| I didn't have to go to class yesterday.
|
3) prohibition (negative)
| You must not open that door.
| ¾
|
4) 90% certainty
| Mary isn't in class. She must be sick. (present only)
| Mary must have been sick yesterday.
|
5) plan; agreement
| We are to meet at nine.
| We were to meet at nine.
|
6) order; instruction
| You must go there at once. You are to go there at once.
| ¾
|
7) destiny (past only)
| ¾
| He was never to see his wife again.
|
If the main verb of the sentence is in the present, no change is made in the verb tense or modal in the object clause.
|
If the main verb of the sentence is in the past, the verb in the object clause is usually also in a past form.
|
He sais (that) he works hard.
| He said (that) he worked hard.
|
He sais (that) he is working hard.
| He said (that) he was working hard.
|
If the action of the object clause is simultaneous with that of the principal clause, the Past Indefinite or the Past Continuous is used in the object clause no matter which Past tense-aspect form is found in the principal clause.
|
He sais (that) he worked hard.
| He said (that) he had worked hard.
|
He sais (that) he was working hard.
| He said (that) he had been working hard.
|
He sais (that) she has already left.
| He said (that) she had already left.
|
If the action of the object clause precedes that of the principal clause, the Past Perfect or the Past Perfect Continuous is used in the object clause no matter which Past tense-aspect form is found in the principal clause.
|
He sais (that) he will work hard.
| He said (that) he would work hard.
|
He sais (that) he will have finished the work by September.
| He said (that) he would have finished the work by September.
|
He sais (that) he will be working hard all day long.
| He said (that) he would be working hard all day long.
|
If the action of the object clause follows that of the principal clause, the Future- in-the-Past or one of the other means of expressing future actions viewed from the past is used in the object clause no matter which Past tense-aspect form is found in the principal clause.
|
He sais (that) he is going to work hard.
| He said (that) he was going to work hard.
|
He sais (that) he can work hard.
| He said (that) he could work hard.
|
He sais (that) he may work hard.
| He said (that) he might work hard.
|
He sais (that) he has to work hard.
| He said (that) he had to work hard.
|
He sais (that) he must work hard.
| He said (that) he had to work hard.
|
He sais (that) he should work hard.
| He said (that) he should work hard.
|
He sais (that) he ought to work hard.
| He said (that) he ought to work hard.
|
The rules of sequence of tenses cannot be observed with certain modal verbs which have only one form. (must, should, ought and need)
|
Infinitive
| Active voice
| Passive voice
| Uses
|
Indefinite
|
to write
to come
|
to be written
—
| the action is simultaneous with that expressed by the finite verb.
|
He wants to write her about it. He wants to be written about it.
|
Continuous
|
to be writing
to be coming
|
—
—
| the action is temporary and not a usual one.
|
He may be writing a new novel.
|
Perfect
| to have written
to have come
| to have been written
—
| the action precedes
that of the predicate.
|
I am glad to have written her about it. I was surprised to have been written about it.
|
Perfect Continuous
|
to have been writing
to have been coming
|
—
—
| the action began before the time indicated by
the predicate and is still going on.
|
He is said to have been writing this novel for 2 years already.
|