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<p>I don’t recall ever having seen it tested, but you never know.</p>
<p>“if” indicates a condition, as in:</p>
<p>“If you eat, I will go hungry” or “I want to go if you come with me.”</p>
<p>“whether” indicates two alternatives, as in (remember that “or not” is implicit and is not needed*):</p>
<p>“I don’t know whether [or not] what he is saying is true” or “I can’t decide whether to eat apples or oranges.”</p>
<p>In some cases, “if” sounds perfectly right to our desensitized ears even when it is not. Here are some common instances of error (most of which have numerous common derivatives that are equally erroneous):</p>
<p>“I am wondering if you could help me.”
“I don’t know if this right.”
“I can’t decide if I should do this.”</p>
<p>To test these out, move the dependent clause that begins with the subordinating conjunction “if” to the beginning of the sentence and see if the sentence is logical**; if it’s not, then “if” is not correct:</p>
<p>“If you could help me, I am wondering.” Incorrect. “wonder” requires an object here, and it doesn’t have one. Moreover, one’s wondering is not contingent upon whether the other helps him or her.</p>
<p>“If this is right, I don’t know.” Incorrect. What don’t you know? Also, the illogical idea that one’s not knowing is dependent upon something’s*** being right is illogical.</p>
<p>“If I should do this, I can’t decide.” Incorrect. One’s inability to decide is not a result of the fact that he or she should do something.</p>
<ul>
<li>There is an exception I can think of to the rule that “or not” is not needed when one would otherwise use “whether or not”: when two items are listed after the “whether” and one wishes to indicate that it’s possible that neither of them could occur, as in: “I can’t decide whether or not to eat apples or oranges.” The meaning here is that one can’t decide whether to have either of those fruits at all; he or she is not deciding between the two fruits.</li>
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<p>** Did you catch the error? “if the sentence is logical” should be “whether the sentence is logical.”</p>
<p>*** This sure sounds wrong, doesn’t it? Well it’s not. :)</p>