Inverted conditionals: should you need, had I known, were it to

The idea

In an inverted conditional, you leave out if and put should, had or were in front of the subject. The should pattern adds should. The meaning stays the same; the style is more formal.

Should + subject: a possible future

It makes the situation sound less likely. People often use it in polite requests and offers.

• Should you have any problems, please contact the office.
• Should your plans change, please let us know.

The main clause can be an imperative, a will sentence or a modal sentence.

• Should it rain, the event will move indoors.

Had + subject + past participle: an imagined past

It replaces if + past perfect in a third conditional. See The third conditional: unreal past situations.

• Had they sold the flat last year, they would have lost money.
• Had she known the risks, she would have refused.

Were + subject + to-infinitive: an unlikely future

It is used for unlikely future situations. See The second conditional: unreal situations now or in the future.

• Were the climate to change faster, many species would die out.
• Were the company to close, hundreds would lose their jobs.

With the verb be, were can start the clause without to: Were I you, I would accept.

Negatives

To make a negative, put not after the subject.

• Had we not left early, we would have missed the flight.
• Should you not receive the letter, please call us.

What comes next

See Zero and first conditionals: real conditions, The second conditional: unreal situations now or in the future, The third conditional: unreal past situations and Mixed conditionals: when the time is different in the two parts. For other kinds of inversion, see Inversion for emphasis.