最近有网友分别提问，问及下例句子中的than分句如何分析结构：
1 The result will be less effective than would be achieved by a teacher in harmony with the unit.
2 This meat is better than was ordered.
3 This chicken is better than we had last week.
在分析这个几个句子之前，我们先看看另外二个句子：
比较分句than what中的what应该保留还是删去
■曹荣禄
最近有网友分别提问，问及下例句子中的than分句如何分析结构：
1 The result will be less effective than would be achieved by a teacher in
harmony with the unit.
2 This meat is better than was ordered.
3 This chicken is better than we had last week.
在分析这个几个句子之前，我们先看看另外二个句子：
4 He has more books than what I have.
5 Much fewer tickets were sold than what were available.
我们知道，这二个句子中的加粗部分为主句中的比较项（comparative phrase）, 比较项的对应项（counterpart to the comparative phrase）在比较分句中是必须省略的，在从句中形成一个空位（gap）。即than分句必须是一个结构不完整的分句，由比较对应项所充当的那个分句成分缺失。
句4中，比较对应项为have的宾语，必须省略，但该句what作了have的宾语，比较分句没有空位，故为语法错误。句5中，比较对应项在比较分句中作主语，必须省略，但该句用what作了主语，分句没有空位，也是语法错误。所以以上二句中的what 均应删去，才是语法正确的句子。
但是，Swan的《英语用法指南》和Huddleston的《剑桥英语语法》均指出，在英语的有些方言中，的确有句4和句5这样的句子。What的这种用法属于方言，是不规范的英语（non-standard English）,应该避免。WR网站的老外几乎一致认为句4和句5这样的句子中的what是错误的，他们是不会使用what的。
可能正是由于这种what占据了本应省略的空位的位置，形成语法错误，以致于有些人潜意识中认为than后接what为语法错误，因而遇到than what时就不假思索地省略what, 导致出现了句1、句2、句3这样的句子。即在本该使用what的地方，错误地省略了不该省得what, 导致句子结构错误，缺少了必要的分句成分。这样的句子属于母语人士犯的语法错误。
如果我们仔细分析句1-3，我们会发现其共同点：主句为主系表结构，形容词比较级作表语，为比较项。但than分句中缺少的主语并不是比较对应项，比较分句中的比较对应项仍然在从句中作表语且必须省略形成空位，从句省略了系词be, than后面为比较分句的主语。《剑桥英语语法》指出，只有在二种情况下比较分句才能省略主语而保留谓语动词：1）主语为比较对应项；2）主语为嵌入分句。句1-3的than从句中省略的主语既不是比较对应项，也不是嵌入分句，故主语的省略为语法错误，应该补上不该省略的主语what (或名词+关系代词)。
1a) The result will be less effective than what / the result that would be
achieved by a teacher in harmony with the unit.
2a) This meat is better than what / the meat that was ordered.
3a) This chicken is better than what / the chicken we had last week.
《剑桥英语语法》1121页给出了下面例句：
This result is better than __ would
probably be achieved by a vaccination policy.
The price was higher than he wished to
pay __.
对此，作者评论道：The missing element from the
comparative clause must be understood as an NP, not an AdjP: they are
equivalent to “…than the result that
would probably be achieved…”, “…than the price that he wished to pay”. It
is questionable whether such examples are frequent and systematic enough to
qualify as grammatical; certainly the construction illustrated here is
generally not permissible, as is evident from the ungrammaticality of *This candidate was much better qualified
than they appointed (“than the one whom”), and the like.
Fowler在《现代英语用法词典》中也给出类似说明：
