Obligation:
Must
for strong obligations which express the
authority of the speaker or writer.
·
A for formal rules
or laws.
·
B for suggestions,
advice or recommendations that the speaker or writer feels strongly about.
Have
to for strong
obligations which express
the authority of a third person, rather than that of the speaker or
writer
·
When the speaker
wants to show they are not responsible for imposing the obligation, or does not
agree with it.
·
When the speaker or
writer is reminding someone about a rule or law.
Have
got to is more informal than Have to.
·
For direct commands
·
For emphasis
Need
to to express needs or necessities rather than
strict obligations
Negative
forms
Musn’t expresses prohibition – negative rules and laws or strong
advice.
Don’t
have to / have not got to - lack of obligation or necessity
Do not
need to / Needn’t lack of obligation or necessity and are
similar in meaning to don’t have to.
Did not
need to + infinitive means: “It was not
necessary, so we didn’t do it”
Needn’t
have + past participle means: “It
was not necessary, but we did it in spite of this”
Permission
and Prohibition
Can /
can’t commonest way of expressing permission and prohibition.
May I ..?
means the same as Can I…? but more
formal and more polite.
Other
expression of permission and prohibition
·
be allowed to +
infinitive
·
be permitted to + infinitive
·
let + infinitive
without to
Other expressions of prohibition:
You aren’t allowed to …
Smoking is not permitted in…
You are not permitted to
smoke…
People are forbidden to
smoke…
The workers have been
prohibited from …
Nigel has been banned from
driving….
