肯定句改否定句是句型转换中常用题型，但初学者往往出错，现选
几例通过比较，说明其正确的改法。
例1：I thought she was there.
(误)：I thought she wasn't there.
(正)：I didn't think she was there.
例2：I thought he was right.I thought he was right.
(误)：I thought he wasn't right.
(正)：I didn't think he was right.
1.通过上面两例说明一条规律：
英语中,象think(认为)、believe(相信)、expect(盼望)
suppase(推测)、imagine(想象)等表示揣测或信念的动词。后接that
引导的宾语从句时、改为否定句时,按习惯把that从句中的否定式移到
主句。(即：否定主句谓语，而不否定从句谓语。)
例1：He can sing this song and that one.
(误)：He can't sing this song and that one.
(正)：He can't sing this song or that one.
例2：He can read and write.
(误)：He can't read and write.
(正)：He can't read or write.
2.说明：肯定句中的连词and在否定句中一般要用or.
例1：Tom went to school，too.
(误)：Tom didn't go to school，too.
(正)：Tom didn't go to school，either.
例2：He has been to Beijing,too.
(误)：He hasn't been to Beijing,too.
(正)：He hasn't been to Beijing,either.
3.以上两例说明：肯定句中的too、also，在否定句中应改为either.
例1：He has had supper already.
(误)：He hasn't had supper already.
(正)：He hasn't had supper yet.
4.上例说明：随着对谓语动词的否定,某些动词也要作相应的变化。
例1：He had a good rest just now.
(误)：He hadn't a good rest just now.
(正)：He didn't have a good rest just now.
5.上例说明：have在(开会、吃饭、休息、进行体育锻炼)这些词组
中是行为动词，否定句应加助动词来完成。
例1：He used to live there.
(误)：He didn't used to there.
(正)：He used not to live there.或
He never used to live there.
6.上例说明：used to(过去常常、习惯于…的)的否定式一般不用did构成，
used to的否定式应为used not to或never used to.
例1：Let's sit here.
(误)：Let's don't sit here.
(正)：Let's not sit here.或
Don't let's sit here.
例2：Let's do it.
(正)：Let's not do it.或：Don't let do it.
7.上两例说明：let后接的是不带to的不定式，变为否定式时，直接在句首
加don't或在不定式后加not.
例1：You had better come.
(误)：You didn't have better come.
(正)：You had better not come.
8.上例说明：had better相当于一个情态动词，不可分割。因此not应放
在其后，would rather也是如此。
例1.Be here early tomorrow.
(误)：Be not here early tomorrow.
(正)：Don't be here early toworrow.
9.上例说明：第二人称祈使句的否定，一般在谓语动词前加Don't.
例1.I saw both the teacher andthe students.
(误)：I didn't see both the teacher and the students.
(正)：I saw neither the teacher nor the students.
10.上例说明：含both..and..或not only..but also..的否定语
应用neither..nor..的形式。
例1.Both Tom and Xiao Ping went to school.
(误)：Both Tom and Xiao Ping didn't go to school.
(正)：Neither Tom nor Xiao Ping went to school.
例2.I know all these words.
(误)：I don't know all these words.
(正)：I know none of these words.
例3.Every student can answer it.
(误)：Every student can't answer it.
肯定句改否定句容易错的地方
11.通过上面三个例句说明：一个句子里如果含有不定代词both、all、every时，改为
否定句时要把这些不定代词改为相应的表示否定意义的不定代词。
例1.She always finishes her homework in time.
(误)：She doesn't always finishes her homework in time.
(误)：She doesn't always finishes her homework in time.
(正)：She never finishes her homework in time.
例2.It often rains here.
(误)：It doesn't often rian here.
(正)：It seldom rains here.
例3.I nealy saw everythings.
(正)：I hardly saw angthings.
12.以上三例说明：主谓之中有一个副词的句子，英语习惯上不是在副词后面加not，
而是把这个句子中的副词改为一个相应的表示否定的副词，全句就变成了否定句。
各种时态肯定句变否定句口诀
变成否定有规则，
"是""将""有"后加not。
假如没有"是""将""有"，
动词前面加don't(doesn't/didn't)。
be的各种形式：am is are was were.
have(有)的各种形式：have has had
情态动词：shall can may must could would should
助动词：be have do.
如果肯定句中有以上四种特殊定式动词，就直
接在这些词之后加上否定词not (never,no)即可。
。