'If' versus 'Whether'

[Gray]

Which is correct?

1) I am not sure whether I understand this.

2) I am not sure if I understand this.
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First lesson - English, not english. I, not i. ~A student of English

[Snoowoo]

both of them are correct

[SkiIucK]

Both seem reasonable.

[Qadirttt]

yes if this is possible than go for this option.

[Alan]

Hi Gray,

The use of 'whether' introduces the idea of two possibilities. 'I don't know if it's possible' simply means you doubt the possibility of something. 'I don't know whether it's possible' introduces the idea that it may or may not be possible.

Alan
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English as a Second Language
You can read my ESL story Present Simple

[Milanya]

if or whether. In informal writing, both if and whether are standard for introducing a clause indicating uncertainty after a verb such as ask, doubt, know, learn, or see: We shall soon learn whether (or if) it is true. In such contexts, however, the use of if can sometimes create ambiguities. Depending on the intended meaning, the sentence Let her know if she is invited might be better paraphrased as Let her know whether she is invited or If she is invited, let her know.
http://www.bartleby.com/64/C003/0164.html
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con·text - The part of a text or statement that surrounds a particular word or passage and determines its meaning.

[Gray]

[Milanya]

I absolutely agree with Alan that there might be a slight difference in usage. I just see broader possibilities than he has given in his post.
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con·text - The part of a text or statement that surrounds a particular word or passage and determines its meaning.

[Alan]

Good!

Alan
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English as a Foreign Language
You can read my EFL story Progressive Forms