The words 'if' and 'whether' are sometimes interchangeable. However,
this is not always the case.
Whether and If (Interchangeable)
Whether and if can be used
interchangeably in the following circumstances:
When reporting yes/no
questions.
 I am
unsure whether I will be attending the party. 
I am
unsure if I will be attending the party.
(In this example, the yes/no question is "Am I attending the
party?")
Janice
wondered whether she had unplugged the iron.
Janice
wondered if she had unplugged the iron.
(In this example, the yes/no question is "Did Janine unplug the
iron?") |
In
whether/if...or...constructions.
I
would like to know whether it is a true story or fabricated.
I
would like to know if it is a true story or fabricated.
Note: Using 'whether' is far more common. It is certainly more
formal. |
Whether
In the following circumstances, 'whether'
should be used:
To present two
alternatives (neither of which is a condition).
Inform
the clerk whether Mark needs a seat.
(In this example, the two alternatives are 'Mark needs a seat' and 'Mark
does not need a seat'. The clerk is to be informed in either case.)
Inform
the clerk if you need a seat. 
(This sentence is not grammatically wrong, but it does not mean the same
as the first example. In this example, the clerk is only to be
informed if Mark needs a seat. Therefore, Mark needing a seat is a
condition. This is a conditional sentence. See the section on 'If' below.)
Let
Anna know whether the boss is able to go to Crowborough.
(In this example, the two alternatives are 'going' and 'not going'.
Anna needs to know the answer regardless of which is chosen.)
Let
Anna know if the boss is able to go to Crowborough.
(This sentence is not grammatically wrong, but it does not mean the same
as the one above. In this example, Anna needs only to be told if the
boss is going to Crowborough.) |
| After prepositions.
I
would like to talk about whether you are going to California.
(The word 'about' is a preposition.)
At
this point, the flight attendant makes the decision on whether the
passenger stays on the aircraft.
(The word 'on' is a preposition.)
|
Before infinitive
verbs starting 'to' (e.g., whether to ask..).
I have
been thinking whether to grow my own tomatoes this year.
('To grow' is an infinitive verb) |
| When 'whether' starts
a clause that is the sentence subject
or complement.
Whether you sink or swim is not my concern.
('Whether you sink or swim' is the subject of this sentence.)
I
don't care whether you sink or swim.
('Whether you sink or swim' is the complement of the verb 'to care'.) |
In formal writing.
(When if and whether are interchangeable, chose whether in formal
writing.)
I doubt whether
the team will succeed.
Please
establish a committee to determine whether the proposed funding lines are
appropriate. |
If
Use 'if' to introduce a condition (i.e., in a
conditional sentence). In a conditional sentence, a condition has to be
satisfied before something occurs.
Examples:
If you
sing, I'll pay you ten pounds.
Peter
will catch you if you fall.
Whether or Not
Very often, the 'or not' is superfluous (i.e.,
not required). However, when 'whether or not' means 'regardless of
whether', the 'or not' part is required.
Examples:
Reprimand Chris whether or not he is on time today.
('...regardless of whether he is on time today.')
The
parade will go ahead whether it rains or not.
('...regardless of whether it rains.')
(Note: There is leniency on where the 'or not' is placed. It does not have to
follow immediately after 'whether'.)
Select the correct version:
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KEEP IT SIMPLE
Use 'if' to introduce a condition. In all other circumstances, use 'whether'.
A condition is something that must be satisfied before something else occurs.
 If it rains,
bring in the tables.
(If it rains = condition)
Add a point
if I get the right answer.
(if I get the right answer = condition)
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Common grammar errors
