Grammar: Obligation and necessity
There are several ways of talking about obligation and necessity. The following
structures are all followed by the infinitive.
must / mustn’t: We use must / mustn’t to say that something is necessary, often
because the speaker thinks it is.
Example: You must take this your top priority. We mustn’t miss this deadline.
have to: We use have to when the situation or circumstances make it necessary to
do something.
Example: I have to show something to the design group.
Do we have to prepare the schedule or will Dan’s team do this?
don't / doesn’t have to: We use don’t / doesn’t have to to say that something
isn’t necessary. It is not an order or instruction like mustn’t, but instead expresses
an absence of obligation.
Example: You don’t have to finish the report today. Tomorrow will be fine.
The summary doesn’t have to be too detailed. It’s up to you how long to make it.
need to: We use need to in a similar way to have to, to talk about general rules or
the requirements of a situation.
Example: I need to receive your estimate today if you want to be considered for
this contract. Do we both need to attend the meeting?
don’t / doesn’t need to: We use don’t /doesn’t need to in the same way as don’t
/ doesn’t have to to express an absence of obligation.
Example: You don’t need to finish the report today.
The summary doesn’t need to be too detailed.
Task 7 Complete the sentences by underlining the most appropriate form.
1) You don’t need to / mustn’t write the report – I have already done it.
2) You mustn’t / don’t have to smoke anywhere in this zone.
3) I’m a maintenance technician. I must / have to tour my area and I have to /
must check the instrument panels and fill in the records sheets. It’s my job.
4) You don’t have to / mustn’t bring food with you – all meals are provided.
5) You need to / must follow the safety procedures.
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