Here are some more thoughts on the subject. Note that they are what
I think, and so are not to be taken as authoritative.
[FONT="]7.1. IF and WHETHER[/FONT]
- [FONT="]I don't know if/whether Mila is coming tomorrow (or not).[/FONT]
- [FONT="]I am going out if Mila is coming. [/FONT]
- [FONT="]I am going out whether Mila is coming or not.[/FONT]
[FONT="]At first sight there is little difference in meaning in [73] whether we use
IF or WHETHER, though only with the latter does
or not have an acceptable alternative position immediately preceding
Mila. In [74], however, WHETHER cannot be used, and in [75] most native speakers would find
IF unusual. There is clearly, therefore, a difference in meaning between the two words. [/FONT]
[FONT="]With I
F we are considering the uncertainty of a happening or state. This means that we are not certain of its actual happening or state: its non-happening or non-state is a possibility, but that negative situation is not explicitly (or implicitly) considered. Indeed, the negative situation may change the meaning of the utterance as a whole. In [74]
, the speaker states only that in the event of Mila's coming, he is going out. The implication that in the event of Mila's not-coming the speaker will not go out may be intended by the speaker, or such an inference may be drawn by the listener, but it is impossible to say for sure. We have a
double uncertainty: about the happening or state in the
IF-clause, and about the consequence stated in the other clause in the event of non-happening or non-state.[/FONT]
[FONT="]With WHETHER, on the other hand, the negative situation is always implicitly (and often explicitly) stated, and may change the meaning of the utterance as a whole. In [75] there is
certainty that the speaker is going out. The
single uncertainty is about the happening or state in the WHETHER-clause. The two utterances are fundamentally different in meaning, a necessity highlighted by the need to add
or not to the WHETHER-clause [75] and the need
not to add it to the
IF-clause [74].[/FONT]
[FONT="][73] presents a different situation. Here, there is still the same uncertainty about whether Mila is coming. However if the speaker does not know about her coming, then he clearly does not know about her not-coming.
Knowing is not a consequence of
coming, as opposed to
going out in [74], which
is a consequence of
coming. Thus, while the difference in meaning between
IF and WHETHER is the same as ever, the differences in the
practical results of the difference in meanings are minimal. This explains why we can use either word in such
non-consequential statements, and also why
if not is acceptable (or omissible) with both words.[/FONT]
http://www.gramorak.com/Articles/If.pdf