Permission

e.g.You can takemy umbrella.

Can in this meaning is found in affirmative sentences, inter-
rogative sentences in which a request is expressed, and in negative
sentences where it expresses prohibition.

Cf. You can usemy car.
CanI useyour car?
You can't usemy car today.

In this meaning can is combined with the simple infinitive.
The form could with reference to the present is found only in
interrogative sentences in which it expresses a more polite request.

e.g. CouldI useyour car?

The form could is found in reported speech (i.e. in accordance
with the rules of the sequence of tenses).

e.g. He said that I could usehis car.

Heasked me if he could usemy car.

4) uncertainty, doubt,

e.g. Canit betrue?

In this meaning can is found only in interrogative sentences
(in general questions). Besides, sentences of this kind are often
emotionally coloured and so their application is rather restricted.

Depending on the time reference, can in this meaning is used
in combination with different forms of the infinitive.

Thus, if reference is made to the present, the simple infinitive
is found with stative verbs.

e.g. Canhe really beill?
Canit beso late?

With dynamic verbs, the continuous infinitive is used.

e.g. Canshe be tellinglies?

Canhe be makingthe investigation all alone?

Can in combination with the perfect infinitive refers the ac-
tion to the past.

e.g. Canhe have saidit?

Canshe have tolda lie?

The combination of can with the perfect infinitive may also
indicate an action begun in the past and continued into the mo-
ment of speaking. This is usually found with stative verbs.

e.g. Canshe really have beenat home all this time?

However, if can is followed by a dynamic verb the Perfect
Continuous infinitive is used.

e.g. Canshe have been waitingfor us so long?

Could with reference to the present is also used in this way,
implying more uncertainty.

e.g. Couldit betrue?

Couldshe be tellinglies?

Couldhe have saidit?

Couldshe have been waiting for us so long?

In Russian both variants, with can and could, are rendered in
the same way: Неужели это правда?, Неужели она лжет? and
so on.

5) improbability,
e.g. It can't betrue. (Это не может быть правдой. Вряд ли это так.)

In this meaning can is found only in negative sentences, which
are often emotionally coloured. Depending on the time reference,
this can is also used with different forms of the infinitive.

e.g. He can't bereally ill.
She can't be tellinglies.
He can't have saidit.

She can't have beenat home all this time.
She can't have been waitingfor us so long.

Could is also used in this way making the statement less cate-
gorical.

e.g.It couldn't betrue.

She couldn't be telling lies.

He couldn't have saidit.

She couldn't have beenat home all this time.

She couldn't have been waitingfor us so long.

§ 78. Can and could followed by different forms of the infinitive,
are found in special questions where they are used for emotional co-
louring (for instance, to express puzzlement, impatience, etc.).

e.g. What can (could)he mean?
What can (could)he be doing?
What can (could)he have done?
Where can (could)he have gone to?

Itcan be rendered in Russian as: Что, собственно, он имеет
в виду?

§ 79. As is seen from the above examples, the form could refer-
ring to the present is sometimes clearly opposed to can in that it
expresses unreality whereas can expresses reality. This may be ob-
served in the following meanings:

ability — He can speak English.

He could speak English if necessary.

possibility due to circumstances —

You can getthe book from the library.

You could getthe book from the library if necessary.

In the other meanings, however, this difference between the
two forms is obliterated. Could is used either as a milder or more
polite form of can (a) or as a form implying more uncertainty
than can (b):

a) permission — CanI useyour pen?

CouldI useyour pen? (more polite)

b) uncertainty, doubt, improbability —

Canit betrue?

Couldit betrue? (less certain)

It can't betrue.

It couldn't betrue, (less certain)

§ 80- In addition to the above cases illustrating the inde-
pendent use of can, this modal verb occurs in adverbial clauses of
purpose, where it is structurally dependent (for a detailed treat-
ment of this use of can see "Verbs", § 143).

e.g. I'llleave the newspaper on the table so that he can see itat

once.

I left the newspaper on the table so that he could seeit at
once.

§ 81. Note the following set phrases with can:

a) She can't help crying.