Modality and conditionals

collins cobuild grammarThis article has been written by Damian Williams, who is an ELT author and teacher trainer.

Can you imagine what I would do if I could do all I can?

Sun Tzu

 The quote above, attributed to an ancient Chinese military strategist, is often used in leadership training to encourage people to act on their ideas and see them through to completion. But we’re interested in it for another reason: the language it contains, namely modals and a conditional sentence. In this blogpost we’re going to discuss each of these areas of language in turn.


Consider the following statements:

1  Mr Wilkins is the oldest person in the village.

2  Mr Wilkins must be the oldest person in the village.

How many people are referred to (either explicitly or implicitly) in each statement? The correct answer is one person in statement 1, and two people in statement 2. If we rephrase statement 2, it reads something like:

From everything I know about the people in the village, I’m certain Mr Wilkins is the oldest person in the village.

Or even just:

I’m certain Mr Wilkins is the oldest person in the village.

As you can see, there are now two people explicitly referred to in the statement: ‘I’ and ‘Mr Wilkins’. This example is taken from Collins COBUILD English Grammar (2017), which states that:

Modals are mainly used when you want to show your attitude towards what you
are saying, or when you are concerned about the effect of what you are saying on                       the person to whom you are speaking or writing.

This is what all modals share – the fact that they allow us to express our attitude to the facts. Each modal does this in a different way, but in effect every time we use a modal it’s the same as saying I think it’s that … . For example:

It might rain later. = I think it’s possible that it will rain later.

You should eat fewer carbs. = I think it’s a good idea that you eat fewer carbs.

England will win the World Cup. = I think it’s inevitable that England is going to win.

This allows us to understand why some modals and ‘semi-modals’ behave the way they do. For example, must is a modal, i.e. it allows us to say I think it’s obligatory that … . Have to, on the other hand, is not a modal. If we use this to talk about an obligation, it’s seen as more of a fact. Compare these examples:

Helmets must be worn at all times.

You have to eat or you die.

The first statement describes an obligation created and enforced by people – if you don’t, then they will punish you. The second statement describes an obligation created and enforced by nobody, it’s just a fact of life.

In their positive forms, they have fairly similar meanings. But when we look at the negatives, the difference becomes clearer.

You mustn’t use your mobile in the library.

You don’t have to wear smart clothes if you don’t want to.

In the first statement, there is a negative obligation, created by people. In the second statement, there is no obligation. This is why have to is not a modal – its negative form subtracts its meaning rather than negating it.

Another ‘semi modal’ is need, which works both as a modal and as a verb. We can see the difference in the same way when we look at its negative form:

There’s nobody here – we needn’t have arrived so early!

We didn’t need to arrive early so we got there at 9.

In the first statement, need is acting like a modal: we’re saying that we only realized the lack of necessity when we said this sentence (or From everything I now know about the situation, I think it’s unnecessary…). In the second statement, need acts like an ordinary verb, and so, as was the case with don’t have to, the negative form subtracts its meaning rather than negating it.

Another important aspect of modals is how they refer to time, which we discussed in our previous post: tense and aspect. According to Lewis (1986:52):

… modality allows the speaker to introduce a personal interpretation of the non-factual and non-temporal elements of the event.

In other words, modals allow us to express our attitude at the time of speaking. This is important as it helps us understand why modals don’t have past forms. Of course could and would are often used as the ‘past’ forms of can and should, but in fact these behave more like remote forms (see our previous post).

When we use modals to refer to past events, we use the perfect aspect to show that we are expressing our opinion now, referring to a past event. The perfect aspect allows us to link these times:

You could have told me you weren’t coming! = I think (now) it was possible for you to have told me in the past (and it’s annoying me now!)

We should’ve brought more money. = I think now that it would have been a good idea to bring more money.

Another area in which time plays an important role is exemplified by the original quote from Sun Tzu: conditional clauses.


Conditionals are often taught as one of four forms:

Zero conditional: present condition, present result; the situation is certain.

If you heat ice, it melts.

First conditional: present/future condition, future result; the situation is likely.

If she gets here on time, we’ll start as planned.

Second conditional: present/future condition, present/future result; the situation is hypothetical.

If Jack did more exercise, he’d lose weight.

Third conditional: past condition, past result; the situation is hypothetical.

If my parents hadn’t met, I wouldn’t have been born.

With this in mind, consider which type of conditionals these are:

If Sally would make more of an effort, she’d have more friends.

If he’s arrived, I’ll speak to him.

If you were going to speak to me like that, I’d tell you to stop.

If Tony hadn’t asked for a place, he wasn’t going to get one at all.

While they don’t fit the ‘rules’ above very nicely, these are all perfectly acceptable sentences. Perhaps more useful is to look at the function of conditional clauses in general terms. Collins COBUILD English Grammar states:

When you want to talk about a possible situation and its consequences, you use a conditional clause.

It then goes on to make the distinction between situations that sometimes exist or existed, situations that you know do not exist and situations that may exist in the future.

This is a useful distinction to make in terms of how we teach conditional clauses – those which talk about real possibilities and those which discuss hypothetical reasons. This then allows us to open up even more language, such as:

A:         I wish it was Saturday.

B:         Why?

A:         Because if it was Saturday, I’d be lying on the beach right now.

The forms I wish + past tense and If + past tense are often taught separately, but in real life they often co-occur in this way, with the latter clause providing further details, and extending the discourse.

Of course, if we have also introduced the idea of remote forms to our students (see our previous post), then we are already halfway there in understanding how these hypothetical clauses are used.

Both modals and conditionals are rather grey areas which can be difficult to fully understand. However, by keeping in mind that all modals have a common function, and by not getting too dragged down with questions of form when we look at conditionals, we can begin to shed more light on these areas of language.


Explore this topic in greater detail with our free guided worksheet.




Lewis, M. 1986 The English Verb: An Exploration of Structure and Meaning LTP


Further reading:

Greenbaum, S., Leech, G., Quirk, R. and Svartvik, J. 1985 A Comprehensive Grammar of the English Language Longman