From the Mailbag

Keith,

In most cases, using "if" for "whether" produces no ambiguity, because there is enough context to decide.

But here's a counterexample:

[*] Let me know if you are free to participate.

This could mean either

[1] If you are free to participate, let me know (that you are free to participate); otherwise, do nothing.

[2] Let me know whether you are free to participate.

In the case that you are not free to participate, [2] requests action by you, but [1] does not.

Mark Spahn (West Seneca, NY)