A reader writes:
A colleague at work says the following sentence is incorrect: “Promotion depends on if the employee maintains a good attendance record.” I don’t see anything wrong with it. Is she just being disagreeable?
I can’t say whether the colleague is being disagreeable or not, but I can say why she objects to the sentence. The conjunctions if and whether are often used interchangeably. Sometimes such usage can pass, but sometimes whether is the only choice.
One rule often cited is that if does not follow a preposition. Corrected, the sentence is “Promotion depends on whether the employee maintains a good attendance record.”
Seeking to avoid confusion, Sir Ernest Gowers added this entry to the 1963 edition of Fowler’s Modern English Usage:
To avoid possible ambiguity it may be prudent to confine if to its proper duty of introducing the protasis of a conditional sentence, and not to use it as a substitute for though or whether or (with not) to introduce a possible alternative.
Note: In the context of grammar, protasis is “the first or introductory clause in a sentence, especially the clause which expresses the condition in a conditional sentence.”
The Chicago Manual of Style spells out two instances in which if should not be used in lieu of whether:
1. to introduce a noun clause in an indirect question the answer to which is either yes or no.
INCORRECT: He asked if his tie was straight.
CORRECT: He asked whether his tie was straight.
The only possible answer is yes or no.
2. to avoid ambiguity.
INCORRECT: Call me to let me know if you can come.
CORRECT: Call me to let me know whether you can come.
With if, two interpretations are possible:
1. Call regardless of your answer.
2. Call only if you will be coming.
By using whether, the speaker makes it clear that a call is desired, regardless of whether the person is coming or not.
Chicago includes three other notes on the if/whether dichotomy in the “Good usage versus common usage” section:
determine whether; determine if.
The first phrasing is irreproachable style; the second is acceptable as a colloquialism. The same is true of decide whether versus decide if.
doubt that; doubt whether; doubt if.
Doubt that conveys a negative sense of skepticism or questioning: “I doubt that you’ll ever get your money back.” Doubt whether also conveys a sense of skepticism “The official says that he doubts whether the company could survive.” Doubt if is a casual phrasing for doubt that.
question whether; question of whether; question as to whether.
The first phrasing is the best, the second is next best, and the third is to be avoided.
Paul Brians (Common Errors in English Usage) acknowledges that if “can’t really be called an error,” but adds, “when you are discussing two alternative possibilities, whether sounds more polished.”
A note by David Foster Wallace in the Oxford American Writer’s Thesaurus offers “a simple test”:
If you can coherently insert an “or not” after either the conjunction or the clause it introduces, you need whether.
He gives these examples:
He didn’t know whether [or not] it would rain. YES
She asked me straight out whether I was a fetishist [or not]. YES
We told him to call if [or not] he needed a ride. NO
If is used to express a conditional.
Whether is used to introduce alternative possibilities.