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Page history last edited by Béatrice H. Alves 14 years, 9 months ago





“If Beethoven had been killed in a plane crash at the age of 22, it would have changed the history of music... and of aviation.” Tom Stoppard

Engineers like to solve problems. If there are no problems handily available, they will create their own problems.” Scott Adams




Conditional sentences: What for?


Usually, conditional sentences are needed when we want to describe a flow chart, handle tables of truth, talk about the technique of troubleshooting, have a briefing about the alternatives to be chosen in case of bad weather, emergencies, etc.


So many things depend on others. And that's when a conditional sentence can be our best tool.


Two Parts of the sentence



When we think in conditional sentences, we usually think in 2 different things:

-         a hypothesis which corresponds to the IF clause.

-         a result which can be a general truth, a probable result, or a hypothetical result in the present or in the past. That’s the main clause of the sentence.



The IF clause can come first or second in the sentence:

I’ll talk to the design team if I have time later today.

If I have time later today, I’ll talk to the design team.

When the IF clause comes first in a sentence, it is followed by a comma ( , ).


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The IF clause structure


It is usually called IF clause but can also be introduced by unless, suppose, as long as, or provided that. (see conditional clauses without if below)


Real conditions in the present

(Present factual conditionals)

IF + subject +
verb in the present

If air expands, …

If a pilot has ultimate control,

If you are a chemist, …

If your field is biology, …

If you have other interests outside science, …

If you’re interested in energy, …

But if you want to do well, …


Real conditions in the future

(factual conditionals)



IF + subject +
verb in the present

If you increase the weight, …

If we don’t fix this problem, …

If we reduce the cost of the materials, …

If we make a higher-quality product, …

If we forget about this design and start again, …

If we reduce the thickness of the case, …


Unreal condition in the present

IF + subject +
verb in the past

If there were a depressurization, …

If you had too much fuel to land on the runway, …

If you saw a UFO during your flight, …

If you mixed these two chemicals, …

If you didn’t wear security shoes, …

If I weren’t qualified, …


Unreal condition in the past

IF + subject +
verb in the
past perfect
(had + past participle)

If the weather had been warmer that day, …

If Fleming hadn’t noticed the bacteria, …

If you had applied to graduate school, …

If they had started the project earlier, …

If the experiment had gone wrong, …

If they hadn’t provided funding for the project, …

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The main clause structure

General truths and
scientific or
repetitive facts

subject + verb in the present

…, it becomes lighter.

…, he or she takes the final decision on controlling the aircraft.

Ability, possibility, advisability, etc.

subject + modal + verb

…, you could work for a pharmaceutical company.

…, you might find yourself working in the biomedical field.

…, you may find it easier to make a career change.

Instructions and commands


…, learn how to work in a team.

…, think about a career in electrical engineering.


Result in the future

subject + will/won’t + verb

…, the cost will increase.

…, we won’t make the deadline.

will/won’t + subject + verb

…, will this affect the quality?

…, will it be ready in time?

wh-word + will/won’t
+ subject + verb

…, what will they say?

…, how will this affect the cost?

Hypothetical result in the present

subject + would(n’t) + verb

…, the masks would fall.

…, you would dump the remaining fuel.

would(n’t)+ subject + verb

…, would you report it?

…, wouldn’t there be an explosion?

wh-word + would(n’t)
+ subject + verb

…, what would happen?

…, why would I be here?


Hypothetical result in the past

subject + would(n’t) have + past participle

…, the O-ring would not have become brittle.

…, he wouldn’t have discovered penicillin.

would(n’t) + subject + have + past participle

…, would they have accepted you?

…, would they have finished by now?

wh-word + would(n’t) +
have + past participle

…, who would you have called for help?

…, what would we have done?




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Some explanation with examples



  • Present factual conditionals are used to talk about general truths and scientific facts.

    (If air expands, it becomes lighter.)

  • Present factual conditionals can also be used to describe things that happen again and again.

    (If a pilot has ultimate control, then he or she takes the final decision on controlling the aircraft.)

  • Present factual conditionals with modals can be used to express ability, possibility, advisability, etc.

    (If you have other interests outside science, you may find it easier to make a career change.)

  • Present factual conditionals can be combined with imperatives to give instructions and commands.

    (But if you want to do well, learn how to work in a team.)



  • Factual conditionals describe future situations that are real or possible under certain circumstances. The IF clause describes a condition, while the main clause describes a certain or probable result.

    (If you increase the weight, the cost will increase.)



  • Unreal conditionals in the present are used to describe events that aren’t happening or situations that don’t exist in the present. The IF clause describes a hypothetical, i.e., unreal condition, while the main clause describes a hypothetical result.

    (If there were a depressurization, the masks would fall.)



  • Unreal conditionals in the past are used to describe events that did not happen or situations that did not exist in the past. The IF clause describes a hypothetical, i.e., unreal condition, while the main clause describes a hypothetical result.

    (If the weather had been warmer that day, the O-ring would not have become brittle.)


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Deconstructing some previous knowledge



At school, we learn that there are 3 types of conditional sentences:


Type 1:

If I do X, Y will be the result. (If + present, main clause with will+verb) 


Type 2:

If I did X, Y would be the result. (If + simple past, main clause with would+verb) 


Type 3:

If I had done X, Y would have been the result. (If + past perfect, main clause with would have + past participle)




These 3 types do exist but it is NOT as automatic as it seems and there are more options, according to the time of the hypothesis and the time of the main clause.



It’s usually better to think:

. If I do X now or later (it’s possible)

. If I did X now (but I don’t do it)

. If I had done X in the past (but I didn’t do it)



. Y is / might be / could be/ should be / may be / can be / must be / will be the result now or later.

. Y might be / could be / ought to be / should be / would be the result now.

. Y might have been / could have been / would have been the result in the past.


and mix according to your needs since past and present are linked and influence each other.



For instance,

. If I hadn’t forgotten to fill up the tank, I wouldn’t be having a fuel starvation now.

. If it weren’t migration time, the birds would have already left and there wouldn’t be any birdstrike risk now.

. If you drop an object, it falls due to gravity. If you had dropped a hammer in this situation, it would have fallen on your foot and now, you wouldn’t be able to walk.

. If you weren’t an engineer, you wouldn’t have figured this problem out.

. If you didn’t speak English, you wouldn’t have been promoted to your current position.



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Conditional clauses without if



We can use other words instead of if in conditional clauses:




We can use unless to mean ‘if… not’.

Unless the landing gear is down, we’ll perform a belly landing.

Unless we work overtime, we won’t make the deadline.

You cannot work as an air traffic controller unless you provide an official medical certificate.



As/So long as, provided/ providing (that)

We use as/so long as, provided/ providing (that) to mean ‘if but only if’

You can borrow my tools as long as you’re careful with them.

We’ll land in Montreal provided (that) the runway isn’t closed for bad weather.



In case

We use in case to talk about things we do in order to be ready or safe because maybe something else will happen. Compare:

We’ll contact this supplier if we have a problem. (We will wait and see if we have a problem before we contact this supplier.)

We’ll contact this supplier in case we have a problem. (We will contact this supplier now. Then we will already be in touch if we have a problem.)


If a passenger has a heart attack, the crew uses the defibrillator.

In case a passenger has a hear attack, we carry a defibrillator.




We sometimes use and to join two ideas instead of using an if- clause.

Do as I say and you won’t have any problem. (= If you do as I say, you won’t have any problem)



Or (else)

We can use or (else) to mean ‘if not’.

Wear your helmet or (else) you might get hurt. (= If you don’t wear your helmet, you might get hurt.)




We can also use suppose or supposing instead of if, especially in unreal conditions.

Suppose you had a hydraulic failure, what would you do?

Supposing there were a strike, how would production suffer?




We can use should instead of if when we are less sure about a possibility. Compare:

If we have enough time, we’ll attend four workshops. (Maybe we will have enough time.)

Should we have enough time, we’ll attend four workshops. (I really doubt that we will have enough time.)




You may read condition expressed in a formal way by inverting subject and verb. It is only used with had, were, and should and is a rather old-fashioned written form.

Had I known the auditor was coming, I would have collected more data. (= If I had known…)

Should you run into bad weather, we would be here to help you. (= If you ran into bad weather…)


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And a question:

We can use What if in question form to make a suggestion.


What if we got another point of view, watched lessons with other approaches, and practiced a little by visiting the Conditional Plus?


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