Whether or Not

While I'm on the subject of superfluous words, why is it necessary (or is it in fact necessary), to add 'or not' when using the word 'whether'.

Obviously when the condition involves more than 2 choices it's necessary to specify the condition, eg. whether to drive or catch a train (if there are other modes of transport available), but if it's simply a yes or no condition, then sure simply 'whether to catch a train' is sufficient, instead of 'whether or not to catch a train'. This is probably a lousy example, but I'm sure you've got the general idea.

It's a good question. The conjunction "whether" has several related meanings:

1) To introduce a single possibility - "I should find out whether he went to work today." This is almost exactly synonymous with "if", but may have a fractionally more doubtful connotation.

2) To introduce several possibilities - "Whether I sink or (whether I) swim, I'm still taking that new position." "Whether... or" is effectively synonymous here with "no matter if... or".

3) To mean either - "Whether by luck or (whether by) judgement, I backed the winning horse."

I think therefore that when the speaker/writer wants to highlight the fact that there are just two alternatives - black and white, or positive and negative, if you like - then "whether or not" is correct, as per the following example:

I'll be in the office tomorrow, whether I'm ill or not.