Inverted conditionals

English can express a condition without if by moving should, were or had in front of the subject. The result sounds more formal and compact than an ordinary if-clause:

If you should need further information, contact the office.
Should you need further information, contact the office.

The second sentence is not a question. It is a conditional clause with statement meaning and question-like word order. No if remains, and we do not add do: ~~Should do you need further information~~.

Three patterns, three kinds of condition

Should + subject + base verb

Should presents a possible future situation politely or cautiously. It is useful in formal instructions, customer correspondence and offers:

Should any errors remain, please notify the editor.
Should you wish to appeal, the form must be submitted within ten days.

The meaning is close to If you should wish to appeal or, in many contexts, simply If you wish to appeal. After should, use the base verb: Should she need help, not ~~Should she needs help~~. This is not the same as should meaning advice in You should ask the editor.

Were + subject + to-infinitive

For a hypothetical or remote future possibility, use were + subject + to + verb:

Were the company to change its policy, customers would be notified.
Were I to accept the role, I would need more support.

This corresponds to If the company were to change.... The result clause commonly contains would, could or might, but its modal expresses the imagined consequence; it does not have to use would mechanically. For a present unreal situation, were can invert without to:

Were the estimate accurate, the project would still exceed its budget.

The fixed advice phrase If I were you becomes Were I you in a formal style. To express “if it were not for”, write Were it not for your notes, we would have to start again.

Had + subject + past participle

For an unreal past condition, invert had from the past perfect:

If the files had been preserved, the comparison would have been possible.
Had the files been preserved, the comparison would have been possible.

The condition did not happen, and the result describes an imagined alternative. This can combine with a present result in a mixed conditional:

Had I taken the job, I would be living in Madrid now.

The hiring decision belongs to the past; the imagined consequence concerns the present. Check the timeline rather than assuming every had clause must be followed by would have.

Punctuation and meaning

When an inverted condition comes first, use a comma before the result: Should the chair request a recount, the figures can be checked again. When the result comes first, a comma is usually unnecessary: The figures can be checked again should the chair request a recount.

Do not use inversion with every kind of conditional. Ordinary if remains necessary in patterns that do not begin with should, were or had:

If the weather improves, we will reopen the garden.
Not: ~~Improves the weather, we will reopen the garden.~~

The patterns have a formal register. In a conversation with a friend, If you need anything, call me is usually more natural than Should you require assistance, contact me. The formal version is useful when it suits the audience and purpose, not as decoration.

Variations worth recognising

The three opening auxiliaries can combine with negatives and longer subjects:

Had I not received your message, I would have gone to the wrong address.
Were there to be another delay, the contract would allow a refund.
Should the information prove inaccurate, we will issue a correction.

In Had I not received, the condition is a past counterfactual; in Were there to be, it is a remote possibility; in Should ... prove, it is a possible future situation presented cautiously. In each case the subject follows the auxiliary and the rest of the clause keeps its expected form.

A past perfect condition does not require a past perfect result. The timeline determines the result form:

Had they taken the earlier offer, they would be in a stronger position now.
Had they taken the earlier offer, they would have saved money last year.

The first links an unreal past choice to a present result; the second links it to an unreal past result. Similarly, Were it not for the extra funding, the project would stop now refers to a present condition, while Had it not been for the extra funding, the project would have stopped last year looks back at a past one.

Do not confuse conditional inversion with a question. Should you need a replacement, let us know has a conditional meaning; Should you need a replacement? asks whether you need one and requires question intonation and punctuation. The words are the same, but the clause function is different.

In practical writing, the inverted form is most natural in letters, policy language and instructions: Should you have any questions, please contact the course team. In conversation, If you have any questions, just ask is often warmer and less formal.