If and whether

Sir Ernest Gowers:

Care is also needed in the use of if in the sense of whether , for this too may cause ambiguity.

Please inform me if there is any change in your circumstances.

Does this mean “Please inform me now whether there is any change” or “If any change should occur please inform me then”? The reader cannot tell. If whether and if become interchangeable, unintentional offence may be given by the lover who sings:

What do I care,
If you are there?

The Complete Plain Words , rev. Sidney Greenbaum and Janet Whitcut (Boston: David R. Godine, 1988).

Also from The Complete Plain Words
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