English Grammar - SHOULD & MUST

Hey, this is Alex.

Thanks for clicking and welcome to this lesson on "should" versus "must".

Now first of all, thank you to Noera from Brazil for suggesting this lesson.

I hope that I will be able to explain the difference between the two words for you and

every other EngVid user.

Now we have a couple of sentences on the board and they're both using "should" and "must"

in a particular way.

So in the first sentence we have "I should see a doctor" and "I must see a doctor".

Now what do you think is the function of "should" and "must" in these sentences?

So if I tell you "you should see a doctor" or "you must see a doctor", what am I telling

you?

I am giving you advice, okay?

So in these cases, you can use "should" and "must" for advice, for advisability.

Now which one is stronger, "must" is stronger?

"Should" means that I think it's a good idea for you to see a doctor, okay?

I think it would benefit you to see a doctor.

If I say, again the example I have is "I must see a doctor", generally you don't really

give advice to yourself, but in this case it is like that.

So if I tell you "you must see a doctor", I am giving you very strong advice, okay?

So "must" is about 80%, 90% of certainty that you must see a doctor, like 80-90% advisability.

It is very, very serious and you have to, you must see a doctor.

If I say "you should see a doctor", this is maybe about 60% advisability where I am telling

you that I think it's a good idea.

So maybe you have an earache, okay, like a very, very small, not very serious problem,

but you should see a doctor.

It's a good idea, it's good advice for you to see a doctor.

Whereas if I say "you must see a doctor", okay, it means that maybe your arm is bleeding

or you just broke your leg, and if you don't see a doctor there will be negative consequences.

Okay, so you can use "should" and "must" for advice, with "must" being stronger.

You can also use "should" and "must" in a different way.

If I say "he should be sleeping" or "he must be sleeping", in this case I am talking about

degrees of certainty.

Okay, so you can use "should" and "must" to talk about certainty.

So "certainty" refers to how sure you are that something is happening, something must

be happening, or something should happen or must happen.

So in these examples, "he should be sleeping" and "he must be sleeping".

So for example, if you come to class in the morning, and your best friend is missing,

your best friend is not in the class, and I ask you, you know, "where is John?"

You say, "he should be sleeping", which means that maybe today, you know, he had a doctor's

appointment in the morning, going back to the doctor, and his doctor's appointment wasn't

until 10 o'clock, and now it's about 8 o'clock, so he doesn't have to wake up until 9 o'clock.

Okay, you're still with me, right?

Now, if I say, "he should be sleeping", I think, "he is probably sleeping".

So this, your level of certainty is at about over 50%, "he should be sleeping", "I think

he is sleeping".

Here, "he must be sleeping", you are almost certain that he is sleeping.

So for example, if your best friend does not come to class, and I ask you, "where is John?"

You say, "he must be sleeping", okay?

Maybe he went partying last night, he had a very late night, and this morning, he did

not come to class because he is sleeping.

So your degree of certainty with "must" is much higher than "should", okay?

So once again, you can use "should" and "must" either for advice or for certainty.

Now, if you're not sure about these just yet, please check out the quiz on www.engvid.com

and test your knowledge.

Thanks for watching and take care.