if的用法是什么？

Question

如题所述

Answer 1

1.
(表示条件)如果
,主句用将来时，if从句用现在时表示将来
He
will
come
if
you
invite
him.
如果你请他,他会来的。
2.
(表示虚拟)假如,要是
1）时态：可以表示过去，现在和将来的情况。它的基本特点是时态退后。
a.
同现在事实相反的假设。
句型
：
条件从句
主句
一般过去时
should(
would)
+动词原形
If
they
were
here,
they
would
help
you.
b.
表示于过去事实相反的假设。
句型：
条件从句
主句
过去完成时
should(would)
have+
过去分词
If
she
had
worked
harder,
she
would
have
succeeded.
The
rice
would
not
have
been
burnt
if
you
had
been
more
careful.
If
my
lawyer
had
been
here
last
Saturday,
he
would
have
prevented
me
from
going.
If
he
had
come
yesterday,
I
should
/
would
have
told
him
about
it.
含义：He
did
not
come
yesterday,
so
I
did
not
tell
him
about
it.
If
he
had
not
been
ill
and
missed
many
classes,
he
would
have
made
greater
progress.
含义：
He
was
ill
and
missed
many
lessons,
so
he
did
not
make
greater
progress.
c.
表示对将来的假想
句型：
条件从句
主句
一般过去时
should+
动词原形
were+
不定式
would
+
动词原形
should+
动词原形
If
you
succeeded,
everything
would
be
all
right.
If
you
should
succeed,
everything
would
be
all
right.
If
you
were
to
succeed,
everything
would
be
all
right.
3.
是否
=
whether
连接宾语从句
I
wonder
if
she
is
ill.
不知她是否病了。

Answer 2

1）用于条件状语从句中，表示“如果……”，假如主句是表将来的时态，从句中只用一般现在表将来
例：If
you
go
there,
I
will
go
with
you.
2)If
only……
“要是……就好了”
表示一种希望，因此句子要用虚拟
例：
If
only
I
hadn't
been
there
the
day
before
yesterday
！
要是我前天没去那就好了！（对过去的虚拟）
3）Only
if
……
“只有当……才……”
Only
+
状语从句，句子要倒装
例：
Only
if
we
study
hard
,can
we
make
great
progress.

Answer 3

(表示条件)如果
He
will
come
if
you
invite
him.
如果你请他,他会来的。
(表示虚拟)假如,要是
If
I
were
you,
I
would
never
do
that.
如果我是你,我决不做那件事。
(表示让步)即使
We'll
go
even
if
it
rains.
即使下雨我们也要去。
是否
I
wonder
if
she
is
ill.
不知她是否病了。
(表示因果关系)每一次...的时候(总是会)
If
I
feel
any
doubt,
I
inquire.
我一感到有疑问就随时询问。
n.
条件;设想[C]
There
are
too
many
ifs
in
his
offer.
他的提议中条件太多了。