If (subordinator)

If is a subordinator similar to whether, marking the subordinate clause as interrogative (e.g., I don't know if that works).

As a subordinator, if has no conditional meaning (for that, see if (preposition)). Instead, it introduces subordinate closed interrogative clauses. This aligns if with whether, and the two may often be used interchangeably, as in I doubt whether/if that's true. However, if is more constrained. As examples, it can appear neither in the whether or not construction (whether/*if or not the room is ready), nor for a clausal subject (Whether/*If to attend was the question).

Traditional grammar books commonly treat if, often understood as a single word encompassing both this subordinator and the homonymous preposition, as a "subordinating conjunction", a category covering a broad range of clause-connecting words.