they can replace if, mainly in everyday conversation, and are often used without a main clause.

Otherwise is used as a linking adverb and has the meaning of apart from this or if we disregard this:

It can interchangeably be used to mean "if - on condition that"

In formal situations, we can use if + were to when we talk about things that might happen but which we think are unlikely (imagiinary)

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.

these expressions mean without; they are used in second and third conditionals and are usually followed by usually precede a noun phrase.

it makes the condition more restrictive

an in case-clause gives a reason. We can use should after in case.

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.

it can replace if in zero conditionals; in the other types of conditionals, we cannot use when instead of if.

we can use them instead of if to express a condition; note that providing/provided (that) is a bit formal.

if something should happen: