IF-PHRASE? IF-CLAUSE??

If+Adjective / If+Adjective Phrase [simply IF-PHRASE] is different (not entirely) from an IF-CLAUSE [Conditional Clause], since it allows certain words (like the subject+verb) to be opted out from the sentence structure. Such omission of superfluous/extra words that could be understood/inferred from contextual clues is called Ellipsis in English Grammar. It is a cohesive device in linguistics.

1. If necessary [if-phrase], we can always change the dates of our trip.
2. If it is necessary [if-clause], we can always change the dates of our trip.

Sentence 1 = Sentence 2

In sentence 1, the use of the IF-PHRASE permits the omission/removal of subject+verb (it is).

When the if-phrase is expanded [ellipsis not used], it forms the if-clause.

More If-phrases

If necessary

If required

If needed

If need(s) be

🙏 These are often used as modifying phrases for added emphasis.