it emphasises that something will (or will not) happen, would (or would not) happen or would (or would not) have happened whatever the condition is/were.
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if it weren’t for/if it hadn’t been for, but for
these expressions mean without; they are used in second and third conditionals and are usually followed by usually precede a noun phrase.
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if in doubt, if possible, if necessary…
we can make the if-clause shorter, by omitting the subject and the verb be; in certain idiomatic expressions, the subject and be are normally omitted.
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in case
an in case-clause gives a reason. We can use should after in case.
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Only If
it makes the condition more restrictive
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So/as long as, providing/provided (that
we can use them instead of if to express a condition; note that providing/provided (that) is a bit formal.
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Suppose/supposing, What if
they can replace if, mainly in everyday conversation, and are often used without a main clause.
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Unless
it appears before an affirmative verb to express if … not.
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When
it can replace if in zero conditionals; in the other types of conditionals, we cannot use when instead of if.
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Provided that / Providing that
It can interchangeably be used to mean "if - on condition that"
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in the event of
if something should happen:
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If + were to
In formal situations, we can use if + were to when we talk about things that might happen but which we think are unlikely (imagiinary)
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Or / otherwise
Otherwise is used as a linking adverb and has the meaning of apart from this or if we disregard this:
