Should vs Need vs Have To vs Ought vs Must

Lesson Transcript

Hi, everybody! My name is Alisha.

In this lesson, I'm going to talk about the differences between “should,” “have to,” “need to,” “ought to,” and “must.”

Let's get started!

Let's begin on this side of the board with “should” and “ought to.”

In this lesson, I'm going to focus on example sentences that use “should.” You may see “ought to” in books or maybe in newspapers from time to time, but in most cases, in everyday Modern American English, we use “should.” We do not use “ought to” very much. It sounds a little bit old-fashioned. So you can replace “should,” in my example sentences with “ought to,” but keep in mind that might sound formal or old-fashioned or a little unnatural in today's English.

So, we use “should” to express advice, general advice. When we want to share our opinion or an idea about something, we can use “should” to do that in a friendly and efficient way. When we make sentences with “should,” it follows this pattern:

[subject] + [should] + [the infinitive verb]

If we want to make a negative statement, we use:

[subject] + [shouldn't] (which is the reduced form of “should not”) and [the infinitive verb]

So, this is present tense, to make a present tense advice statement, we use this pattern.

Let's look at some examples.

First:

“You should start a business.”

Subject [you] should (here, my advice), my infinitive verb is “start.”

“You should start a business.”

I think it's a good idea for you to start a business. That's what this means.

The second example:

“He shouldn't wear that shirt.”

We have the negative “shouldn't,” should not reduces to shouldn't. My infinitive verb is “wear,” wear, not /weer/, “wear.”

“He shouldn't wear that shirt.”

So, maybe, I think the shirt looks bad or maybe the shirt is not appropriate for the event.

“He shouldn't wear that shirt.”

“He shouldn't wear that shirt” is my advice.

Third example:

“They should bring drinks.”

“They should bring drinks,” maybe to a party, for example.

So, “should,” I'm using a positive here. My verb is, “bring,” the infinitive form.

“They should bring drinks.”

You could say, “They should bring drinks to the party,” for example as well too.

The final present tense example is:

“We shouldn't buy any more food.”

So, this is like advice for you and someone else, maybe in a group of people. You have enough food, so negative, “we shouldn't,” we should not “buy” [is my verb] any more food. Any more food means we bought some food. We do not need to buy more food. We shouldn't buy any more food is how a native speaker would say this.

So, let's compare this then to past tense. If you want to use “should” in the past tense, you can use this pattern.

[subject] + [should] + [have] + [the past participle form of the verb]

So here is the change. We need to include “have” and we need to change the verb form.

So, just a couple of quick example sentences.

Here:

“You should have started a business.”

So, that means in the past, at some point in the past, you should have started a business. That's my advice for you in the past. I think it would have been good, it would have been a good idea.

So, ”You should have started a business.”

Or…

“They should have brought drinks.”

So that means, in both of these cases, this thing did not happen in the past, but thinking about it now, it would have been a good idea. That's my advice. They should have done something. So, we use this to express regret.

Reminder, past participle verbs are “started” and “brought,” so not in the simple past form here. So, should- “should have started” and “should have brought.”

Again, you could use “ought to” in these cases.

“You ought to start a business.”

Or, “He ought not wear that shirt.”

Or, “They ought to bring drinks.”

Or, “We ought not to buy any more food.”

But this sounds extremely unnatural in American English. It sounds old-fashioned and rather formal, so I don't really recommend using it, but if you see it in your reading, that is what it means.

Okay. Let's move along then to “have to” and “need to.”

So “have to” and “need to” are the same. We can use them in exactly the same way. I focused on “have to” for my example sentences, but we can substitute “need to” for any of these. They have the exact same feel.

We use these to express responsibility, to express responsibility.

“Should” and “ought to” are used to express advice. These are for responsibility.

To make patterns with these, we use:

[subject] + [have to / has to] (depending on the subject) + [the infinitive verb]

In the negative, we use:

[subject] + [don't have to] + [infinitive verb]

Or depending on the subject, again:

[subject] [doesn't have to] [infinitive verb]

So, let's take a look at some examples.

First, my subject is “you,” you.

“You have to come to the office.”

So, “have to,” I have a responsibility to come to the office. So, infinitive verb form “come” here. My subject is different here though, “he,” “she,” or “it.” When my subject is “he,” “she,” or “it,” I need to use this “has to” pattern or in the negative, “doesn't have to.”

So, “He doesn't have to wear that shirt.”

“He doesn't have to wear that shirt.”

This means he has no responsibility to wear that shirt.

“He doesn't have to wear that shirt.”

So maybe it's like a company uniform, but today, he doesn't have to wear that shirt.

So he has no responsibility to wear that shirt.

Please keep in mind, for this, for this negative portion, we use these for responsibilities, yes, responsibilities that can reasonably be expected. So, sometimes, I hear students use odd negative patterns like “I don't have to drink alcohol at work,” but it's not an expectation, it's not a reasonable expectation to drink alcohol at work, unless maybe like you're a bartender or you work in a bar or something like that.

So when you use “don't have to” or “doesn't have to,” it should be for some reasonable expectation for your life or for the person's life. So, in this case, “He doesn't have to wear that shirt” is probably a situation like I said, like maybe he has a company uniform, but for today's event , he doesn't have to wear the shirt. So, it's kind of a special event.So please keep this in mind when you're using the negative form.

The next example sentence:

“They have to bring drinks.”

So, their responsibility is to bring drinks.

“They have to bring drinks.”

Finally:

“We don't have to buy any more food.”

So, that means we bought some food and now, we don't have any responsibility, there's no responsibility to buy more food. So, we already bought some, we do not have a responsibility to buy more. So, we say, “We don't have to buy any more food.”

Okay. So, when we make the past tense form here, we change this to:

[subject] + [had to] (so the verb “have” changes to “had to) and [the infinitive verb form]

In the negative, we use:

[subject] + [didn't have to]

Didn't have to. So please note, “have” does not change here, so not “didn't had to,” “didn't have to,” didn't have to.

Some examples:

“You didn't have to come to the office.”

So, that means, maybe the person did come to the office and maybe the person's boss is in the office and says, “Oh, you didn't have to come to the office,” meaning you had (past tense), you had no responsibility to come to the office today. Maybe the person came in on a Saturday, for example.

“You didn't have to come to the office.”

Past tense, but that person probably did come to the office.

Another one:

“They had to bring drinks.”

So, their responsibility, their past responsibility was to bring drinks to the party maybe.

“They had to bring drinks.”

So, that was their job or their task or whatever. If we want to express it in past tense, we use this form.

Okay. So, finally, let's look at “must,” must. We use “must” for two primary functions.

First is to express a rule, to express a rule. So, this is usually like an official rule, so like police or an airport rule or a company rule or a school rule, something that's kind of official.

We also use “must” to express very strong personal opinions. So “must” sounds a lot stronger than “should.” In most cases, we use “should” to express our general advice, just like everyday opinions, but we use “must” when we have something really strong that we need to share.

So, to make sentences with “must,” we use:

[subject] + [must] + [an infinitive verb]

(to make a positive)

To make a negative, we use:

[subject] + [must not] + [infinitive verb]

So, some examples:

“You must show your passport at Immigration.”

This is a rule.

“You must show your passport at Immigration.”

So, how do you know is it a rule or is it a personal opinion?

Usually, you can tell, you can understand from the context of the situation. So this is a rule. You see this on a sign at the airport. Passengers must show their passports at Immigration. So, from context, you can understand.

The second one:

“He must stop smoking.”

Maybe, this is a doctor or a concerned family member of this person.

“He must stop smoking.”

So, this is strong personal advice, strong personal advice probably.

“They must not wear shoes inside.”

So, maybe this is like a hotel rule, so guests must not wear shoes inside. So, probably a rule posted somewhere.

This one:

“We must not give up.”

Maybe, this is strong personal advice, probably. This is probably not something we would see on a sign. It's probably like a leader saying to his or her team like we must not give up, we must try. So, giving strong personal encouragement, advice.

So, one key point about “must.” I've talked about the past tense forms of “should” and “have to” and “need to” and all that, we don't have it for “must.” I know that there is this pattern, “must have” and “must not have,” but this is not the past tense of “must.” It’s used to mean something totally different.

“Must have (something, something, something)” means there's a high level of certainty about something in the past.

“Oh, I must have forgotten my keys,” means there's a high level of certainty that I forgot my keys. So, “must have (something)” does not mean “must” in this meaning. It's a different meaning. I'm expressing a guess with a high level of certainty about something that happened in the past.

In the negative form, “must not have” means something in the past was almost certainly impossible.

For example:

“Ah, I must not have sent that email!”

“I must not have sent that email!”

So, that means there's a very- I'm making a guess, again. There's a very high level of certainty that I did not do that thing, that that thing was not done. It was not- it did not happen. It was impossible. So, “must not have sent that email.”

“Oh no, I forgot. I must not have sent that email. I'm so sorry.”

So, these do not refer to the past form of “must.” We don't have that. We're just- when we express a rule, we don't use it in past tense. The rule is forever, so we use this present tense format to do it.

So, this is a quick introduction to the differences between “must” and “need to” and “have to” and “should” and “ought to” a bit too. So, please remember, try to remember the differences between these when you're talking about responsibilities, advice, and rules. I hope that it was helpful for you.

Thanks very much for watching this lesson and I will see you again soon. Bye-bye!

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