Must, should, or ought to?
A woman’s place is in the bosom of her family; her thoughts ought seldom to emerge from it.
The Edinburgh Magazine and Literary Miscellany, Volume 97, 1825
Those nineteenth-century moralists! Can you imagine what today’s world would have been like if women such as Florence Nightingale, Emmeline Pankhurst, or Harriet Beecher Stowe had confined their thoughts to family life? While the viewpoint behind it may be outdated, this famous quotation is a neat way of illustrating one of the main uses of ought, namely expressing the speaker’s view as to a correct or dutiful course of action, often imbued with a tinge of social rectitude.
As you may know, ought is a special type of verb known as a modal verb: I’ve covered some of these already in earlier blogs. I’d now like to turn my attention to a trio of modals which share a similar range of meanings: must, ought, and should. All these verbs can be used to talk about duty and obligation, to give advice or instructions, or to express degrees of probability. Should can also be used in other ways, but as I’m endeavouring to keep this fairly brief, I’ll save my discussion of conditional meanings of should and the difference between should and would for another day. If you’re avid for all the information right this minute, you can find a full rundown of should here.
Let’s explore the central meanings of must, should, and ought first, then we’ll turn to their similarities and differences, so as to help you use each verb in the most effective and idiomatic way.
We use must in three main ways:
• to talk about something that has to be done because it’s compulsory or obligatory (that is, it’s absolutely necessary to obey a rule, law, order, or instruction):
Online stores must give a cooling-off period of seven working days.
She was told that she must not discuss the case with third parties, including her MP.
or because it’s very important:
To calm public opinion, police must quickly arrest the culprits and solve this case.
I must get back to work: a deadline approaches.
• to express the view that something is highly likely because it’s a logical conclusion based on something else that the speaker knows, or it’s the normal thing to expect:
Our measurements show that exactly the opposite must be the case.
Her mega hairdo must have taken several cans of hairspray to achieve.
• to say to someone that you strongly recommend or advise something because it’s a good idea:
If you go to Barcelona, you must see the cathedral.
We get on well and keep saying we must meet up for lunch sometime.
We use ought in three main ways:
• to express the view that something is the right thing to do, because it’s morally correct, polite, or someone’s duty:
You ought to admit that you made a mistake.
They ought not to be allowed to damage property without paying compensation.
• to predict that something is fairly likely or expected, based on normal circumstances or logic:
Our long-delayed mail is on the way from France and ought to arrive today.
The weather oughtn’t to be cold in May.
• to offer or ask for advice or recommendations:
If you haven’t read the book then you ought to see the movie.
What ought to be done to improve things?
Here are the three main meanings of should:
• to talk about what we think is the right or correct thing to do, especially from the point of view of duty or appropriateness:
All employees should be provided with a proper job description.
Children shouldn’t be allowed to watch too much TV.
• to give or ask for advice or suggestions:
I told Kathy she should try to get some rest.
Can you recommend any exercises, or should I see a doctor?
• to predict that something will probably happen or is expected to be the case, based on logic or a typical situation:
My sister’s on her way, she should be here soon.
By next month I should have enough money to buy a car.
Differences and similarities
We can compare and contrast must, ought, and should according to two categories: meaning and grammar.
As we’ve seen, we can use all three verbs to express broadly similar meanings: the main distinctions between them are related to degrees of emphasis. Must is the most emphatic: you use it when you’re confident about a conclusion, or when you want to stress that it’s very important for someone to follow your recommendations. You also use must to refer to something that’s required by a rule or law. Unlike should and ought, must isn’t used to make predictions:
✓ According to the forecast, it should be warm tomorrow.
✓ According to the forecast, it ought to be warm tomorrow.
X According to the forecast, it must be warm tomorrow.
Ought is less strong than must, and isn’t used to talk about things that are compulsory. It often carries with it slightly more forcefulness and more of a sense of moral obligation or appropriateness than should.
The meanings of should that we’re addressing in this blog overlap with those of ought, but should is much more common statistically. There are over 2 million instances of should on the Oxford English Corpus, compared with around 71,000 occurrences of ought. In particular, should is much more frequent in questions or negative constructions than ought. Should is the least forceful of the trio: it’s mostly used to make suggestions and more tentative predictions.
Compare the nuances of meaning in the following:
If you have a mole that starts to bleed, you must see a doctor. [it’s vital, as it could be cancer]
The fat content of the cheese must not exceed 44%. [this is to obey a food regulation]
The object of the exercise was to prevent the public from seeing what they ought to see. [it’s morally desirable that people knew]
I ought to eat more fruit and vegetables. [it’s a good idea and will make me healthier]
You should see the size of the crowds he plays in front of! [this is my opinion, but you don’t actually need to see the crowds for yourself]
I think I should go home. [I’m considering this as an option]
Having said this, however, there’s frequently little distinction in meaning between ought and should, and indeed it is possible to have the same interpretation using one or both alternatives. Should is more common in questions, especially in daily conversation: ought sounds rather formal when used interrogatively. Additionally, speakers of North American English tend to use should rather than ought when expressing a negative idea (we shouldn’t turn away from such opportunities rather than we oughtn’t to turn away from such opportunities).
You can form the past tense of should and ought by using have and the past participle of the main verb. We can use this construction to talk about things which were supposed to have been done or have happened (but didn’t) or to speculate about things which we’re not sure about in the past:
They should have done more research.
I ought to have left here by 3.30.
Surely they should have got home by midnight.
You also form the past of must with have plus the past participle of a main verb. You can use must have to express certainty about something in the past, based on logic or normal expectations:
From the evidence of his pupils, he must have been a good teacher.
However, you can’t use must have to talk about something important that should have occurred in the past or something compulsory. If you say:
They must have done more research.
it doesn’t mean ‘they were supposed to have done more research but didn’t’; it means that the speaker is sure that they had carried out more research in order to get to the situation they’re now in.
Ought is unlike most other modals, because we always use the infinitive to when we use it with a main verb. You shouldn’t say:
X I ought eat less meat.
X Ought we visit her soon?
X You ought not miss this play.
You need to use to:
✓ I ought to eat less meat.
✓ Ought we to visit her soon?
✓ You ought not to miss this play.
The only case where you don’t have to accompany ought with to is if there is no other main verb in the sentence or clause:
✓ Say what you have to say, not what you ought.
✓ We should file that under ‘Educational’ too, oughtn’t we?
With should and must, the infinitive to isn’t used:
X I should to leave now.
X She mustn’t to discuss the case with anyone.
✓ I should leave now.
✓ She mustn’t discuss the case with anyone.
The above should have helped to clarify these three verbs; you ought now to know how to use them; I must stop writing immediately!
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