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Hi, I’m Oli.
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Welcome to Oxford Online English!
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In this lesson, you can learn about the verb
'must'.
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'Must' can have many different meanings in
English.
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In this video, you can learn about the different
meanings of 'must', and how to use 'must'
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in English.
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Part one, using 'must' to talk about obligations.
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First, you can use must to talk about obligations
and rules.
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For example:
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"I must remember to call her—it’s her
birthday."
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This is an obligation.
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It’s very important to me.
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"All passengers must hold a valid ticket."
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This is a rule.
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You can't choose to travel without a ticket.
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These are things that it is necessary or important
to do.
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If you must do something, you have no choice.
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When you use must for obligations, it can
mean that the obligation is important to you
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personally.
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It’s not just a rule that someone else made;
using 'must' means that something matters
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to you.
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For example:
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"You must be here on time, otherwise we’ll
miss the start."
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Using 'must' shows that you care about whatever
you’re going to see.
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Maybe you’re going to see a concert that
you’ve been looking forward to for ages,
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and you’ll be really unhappy if you miss
even a minute of it.
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"I must finish this work today."
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Again, this means that I feel strongly about
this.
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Maybe I promised someone that I would finish
it by today, and it’s important to me that
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I keep my promise.
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When talking about rules, we mostly use 'must'
in formal or written English.
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For example:
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"All candidates must show valid ID."
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This is a rule probably in an examination
hall, which of course is a formal setting.
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"Employees must wash their hands before working
with food."
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This could be from a sign in a restaurant
or café.
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Again, this is more likely to be written than
spoken.
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In informal English, we mostly use the verb
'have to' to talk about rules and obligations.
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To review, you can use 'must' to express an
obligation if the obligation is important
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to you personally, or if you want to sound
more formal.
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Part two, using 'must' to talk about prohibition.
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You can use 'mustn’t' to say that something
is not allowed or forbidden.
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This is the opposite of using must to talk
about obligations or rules, and is similar
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in meaning.
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Look at some examples:
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"You mustn’t smoke here."
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That means smoking is forbidden; it’s against
the rules to smoke here.
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"Mobile phones must not be used while the
plane is flying."
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Again, this means that it’s forbidden to
use phones.
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'Must' expresses the idea that you don’t
have a choice.
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If you mustn’t smoke here, then it’s not
OK to smoke, and you don’t have a choice.
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'Mustn’t' with this meaning is similar to
'can’t'.
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With obligations and rules, we mostly use
'must' in formal or written English, and 'have
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to' in informal English, as we said before.
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However, you can use 'mustn’t' in both formal
and informal English.
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Part three: using 'must' to give strong advice.
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'Must' can be used to give someone advice
or a recommendation.
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For example:
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"You must read this book—it’s amazing!"
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"If you go to Paris, you must take a walk
by the river at night."
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"We must hire some new staff as soon as possible."
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In these examples, ''must' has a strong meaning.
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If I say:
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"You must read this book—it’s amazing!"
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I don’t mean that you have an obligation
to read it.
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I mean that I really, really recommend this
book.
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In the same way, if I say:
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"If you go to Paris, you must take a walk
by the river at night."
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This is advice or a recommendation.
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It doesn’t mean that it’s a rule or an
obligation.
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Sometimes, the meaning of 'must' depends on
the context.
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For example:
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"We must hire some new staff as soon as possible."
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'Must' here could mean that hiring new staff
is necessary, and it’s an obligation, or
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it could be a strong recommendation.
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How do you know what 'must' means in a sentence
like this?
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In a sentence like this, in a lesson, where
there’s no context, you can’t say exactly
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what 'must' means.
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In real life, the meaning would depend on
the context: who’s speaking, what the situation
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is, and so on.
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When you use 'must' in this way, you can’t
use the negative.
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There’s no way to use 'mustn’t' to give
advice or make recommendations.
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Only the positive form—'must'—can have
this meaning.
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Part four: using 'must' to talk about logical
necessity.
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Finally, 'must' can be used to make deductions.
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What are deductions?
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Well, look at some examples, and then I’ll
explain what this means:
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"They must be rich.
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Their house is huge!"
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"It must be a difficult exam—only 10% of
candidates pass."
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"It must have rained last night."
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Take the first sentence:
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"They must be rich.
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Their house is huge!"
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Do we know they’re rich?
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No, we don’t know for a fact.
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But, we do know that they have a huge house.
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Huge houses cost a lot of money.
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Therefore, they must be rich.
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We’re sure that they’re rich, because
otherwise they couldn’t afford such a big
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house.
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Compare:
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"They must be rich."
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"They’re rich."
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What’s the difference?
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"They’re rich" is a fact.
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We know they’re rich.
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Maybe you’re their accountant, and you know
all about their financial situation.
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Maybe they told you how much money they have
directly.
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Anyway, however you know, you know they’re
rich.
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"They must be rich" is a deduction.
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You don’t actually know they’re rich.
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You know something else; you know that they
have a huge house and this makes you sure
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that they’re rich.
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Okay, let’s look at another example:
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"It must be a difficult exam—only 10% of
candidates pass."
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Again, using 'must' expresses a deduction.
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If you say this, you haven’t actually taken
the exam.
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You don’t know for yourself that it’s
difficult.
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However, you do know something else: you know
that only 10% of candidates pass, and this
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makes you sure that it’s a difficult exam.
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In our last example:
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"It must have rained last night."
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Did you see it rain?
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No, you didn’t.
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But, you’re sure it rained.
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How?
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Probably, you can see that the ground is wet.
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You didn’t see or hear the rain, but you
can make a deduction from what you see.
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What you see makes you sure that it rained
last night.
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You can also use 'must not' with this meaning,
but you can’t use the short form 'mustn’t'
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in standard English to express the idea of
deduction.
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'Mustn’t' is only used to say that something
is forbidden.
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Okay, that's a strange point, so let's look
at our next topic, which is negatives--part
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five.
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It’s important to remember that when you
use 'must' with different meanings, the negative
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(or opposite) word is also different.
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Okay, let's look at this.
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So, if 'must' is used for obligation, the
opposite would be 'mustn't', or maybe 'can't'.
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The opposite of 'mustn't' for prohibition
would be 'must' or maybe 'have to'.
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The opposite of 'must' for strong advice is
'shouldn't'.
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And for making deductions, the opposite of
'must' would be 'can't', 'couldn't', or maybe
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'must not'.
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For example:
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"Passengers must place bags above the seats."
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Here, 'must' expresses an obligation.
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The opposite would be:
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"Passengers must not place their bags above
the seats."
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Or, if you wanted to explain this rule in
spoken English, you might say:
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"You can’t put your bag above your seat."
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Another example:
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"You mustn’t say anything to her."
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Here, 'must' expresses prohibition.
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The opposite is:
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"You must say something to her."
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Or:
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"You have to say something to her."
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Finally, if you say:
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"He must be awake.
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It’s two o’clock in the afternoon!"
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Here, 'must' expresses a deduction.
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The opposite could be:
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"He can’t be awake.
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He never gets up before the late afternoon."
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Or perhaps:
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"He must not be awake.
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He never wakes up early."
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It’s important to remember that these opposites
are not all the same!
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For example, if you use 'must' to express
prohibition, the possible opposites are 'must'
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and 'have to'.
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This doesn’t mean 'must' and 'have to' have
the same meaning.
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Modal verbs are complicated.
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For now, you need to remember one important
point:
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Different meanings of 'must' have different
negatives.
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OK?
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Good!
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Let’s look at one more point.
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Part six: past forms.
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Like with negatives, if you want to use must
to talk about the past, the past form depends
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on the meaning of 'must'.
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Often, you need to use a different verb.
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Take a look:
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So, 'must' for obligation, the past form is
'have to'.
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'Mustn't' for prohibition, the past form is
'couldn't'.
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'Must' for strong advice or recommendations,
the past form is 'should have'.
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And for making deductions, the past form is
'must have'.
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Using 'must' with a past meaning is only possible
if you are using 'must' to make deductions.
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In all other cases, you need to use a different
verb to talk about the past.
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Let’s look at some examples:
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"We must be there at 9.00 tomorrow."
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This is an obligation.
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In the past, you'd say, "We had to be there
at 9.00 yesterday."
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"We mustn’t smoke in the restaurant."
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That's prohibition.
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The past: "We couldn’t smoke in the restaurant."
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"You must try the stew—it’s delicious!"
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This is advice.
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The past form: "You should have tried the
stew—it was delicious!"
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"They must be on the subway—I can’t get
through on the phone."
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That's a deduction.
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The past form: "They must have been on the
subway—I couldn’t get through on the phone."
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You can see how you need to use different
verbs to talk about the past, depending on
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the meaning of 'must'.
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Okay, finally, let's do a review.
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Let’s review what we’ve studied in this
lesson.
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'Must' can be used to express obligation and
prohibition, to give strong advice, and to
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00:13:19,790 --> 00:13:22,050
make deductions.
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In some cases, 'must' is similar to other
verbs.
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For example, 'must' used to express prohibition
is similar to 'can’t'.
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00:13:32,089 --> 00:13:35,860
However, remember that similar does not mean
the same!
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'Must' is unique, and no verb is ever exactly
the same as 'must'.
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Different meanings of 'must' have different
negative and past forms.
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In other words, the way you use 'must' depends
on the meaning of 'must'.
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You can’t just use 'must' in the same way
in every sentence; you need to think about
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what 'must' means in each case.
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Do you want more practice with this topic?
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Check out the full version of the lesson on
our website: www.oxfordonlineenglish.com.
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The full lesson includes notes and exercises
to help you practise what you’ve learned
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in this class.
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That’s the end of the lesson.
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Thanks very much for watching!
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I hope it was useful for you.
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I'll see you next time!
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Bye bye.18124
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