4.228 saying whether something is possible

'Be able to' and 'be possible to' can be used instead of 'can' and 'could' to say whether or not something is possible.

The subject of 'be able to' and 'be unable to' usually refers to a person or group of people, but it can refer to any living thing. It can also refer to something organized or operated by people, such as a company, a country, or a machine.

The subject of 'be possible to' is always the impersonal pronoun 'it'.

4.229

If you want to say that it is possible for someone or something to do something, you can use 'be able to'.

• All members are able to claim travelling expenses.
• The goliath frog is able to jump three metres or so.

You use 'be able to' with a negative to say that it is not possible for someone or something to do something.

• They are not able to run fast or throw a ball.

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You can also use 'be unable to' to say that it is not possible for someone or something to do something.

• I am having medical treatment and I'm unable to work.
• Terry Wogan is unable to be with us.

4.231

You can also use 'be possible to' to say that something is possible. You usually use this expression to say that something is possible for people in general, rather than for an individual person.

• It is possible to reach Tunheim on foot.
• Is it possible to programme a computer to speak?
• If it is possible to see them, then I would be grateful for the opportunity.

If you use 'be possible to' to say that something is possible for a particular person or group, you put 'for' and a noun group after 'possible'.

• It is possible for us to measure his progress.
• It's possible for each department to support new members.

You use 'be possible to' with a negative to say that something is not possible.

• It is not possible to quantify the effect.

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You can also use 'be impossible to' to say that something is not possible.

• It is impossible to fix the exact moment in time when it happened.
• It is impossible for a European to understand Tewdros.

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To change the tense of 'be able to', 'be unable to', 'be possible to', or 'be impossible to', you simply change the form of 'be' to an appropriate simple tense.

• The doctor will be able to spend more time with the patient.
• Their parents were unable to send them any money.
• It was not possible to dismiss crowd behaviour as a contributing factor.
• It was impossible for the husband to obey this order.

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All modals except 'can' and 'could' can be used with these expressions.

• A machine ought to be able to do this.
• The United States would be unable to produce any wood.
• It may be impossible to predict which way things will develop.

4.235

'Used to' can be used with 'be able to' and 'be possible to'.

• You used to be able to go to the doctor for that.
• It used to be possible to buy second-hand wigs.

For more information about 'used to', see paragraphs 4.258 to 4.262.