whether和  if用法有什么差别？

whether和if都可以引导宾语从句，表示“是否”，在口语或间接引语中两者可以互换使用。如：
I
wonder
if
/
whether
I
can
get
some
advice
from
you.
Ask
him
whether
/
if
he
can
come.
但在有些情况下，whether和if的用法有一定区别。
1.
whether引导的从句常可以与连词or或or
not直接连用，而if一般不能。如：
正：
Let
me
know
whether
you
can
come
or
not.
误：
Let
me
know
if
you
can
come
or
not.
2.
当宾语从句提到句首时，只能用whether引导，而不能用if。如：
正：
Whether
it
is
true
or
not,
I
can’t
tell.
误：
If
it
is
true
or
not,
I
can’t
tell.
3.
whether可以引导带to的不定式，if则不能。如：
正：
I
don’t
know
whether
to
accept
or
refuse.
误：
I
don’t
know
if
to
accept
or
refuse.
4.
whether及其引导的成分可放于介词之后，作介词的宾语，但if不能。如：
正：
I
worry
about
whether
I
hurt
her
feelings.
误：
I
worry
about
if
I
hurt
her
feelings.
5.
whether可以引导从句，作主语、表语或同位语，而if不能。如：
正：
It
was
uncertain
whether
he
would
come.
误：
It
was
uncertain
if
he
would
come.
正：
His
first
question
was
whether
Tom
had
arrived
yet.
误：
His
first
question
was
if
Tom
had
arrived
yet.
正：
We
must
consider
the
question
whether
we
will
take
these
measures.
误：
We
must
consider
the
question
if
we
will
take
these
measures.