Twice/ double
· "twice Y" / "X times Y" can definitely be used as an appositive。
· 注意doubling the increase of 和 double as much as the increase of是两个完全不同的结构。
· 关于twice as many/much as结构：
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· If you say "twice as many", then this construction should be paired with acountable noun.
e.g., twice as many dogs --> "dogs" is a countable noun
· If you said "twice as much", then this construction should be paired with anuncountable noun.
e.g., twice as much water --> "water" is an uncountable noun
· If the noun in question is already an explicitly numerical quantity, then you should use neither "much" nor "many". Instead, you should just use "twice" or "double" by itself.
e.g., twice the increase --> "increase" is an explicitly numerical quantity
· These rules are followed pretty closely.
so, for instance:
twice as much water --> correct, since "water" is an uncountable noun (but is not an explicitly numerical quantity)
twice the water... --> incorrect, since water is not a numerical quantity
twice as much as the increase... --> incorrect; redundant
twice the increase... --> correct
4. 关于类似twice as many/much as的结构：appositive modifier(同位语修饰词)。
不仅仅名词，有些形容词也是可以作为appositive modifier的，这种形容词用逗号隔开放在句尾，还是习惯于修饰最近的词语(但是不绝对)。这样的形容词有different from, (double/twice) as many as等。
一道来自Manhattan的模考题：
Antigenic shift refers to the combination of two different strains of influenza; in contrast, antigenic drift refers to the natural mutation of a single strain of influenza.
A. influenza; in contrast, antigenic drift refers to the natural mutation of a single strain of influenza
B. influenza, different than the natural mutation of a single strain, known as antigenic drift
C. influenza, in contrast to the natural mutation of a single strain, known as antigenic drift
D. influenza, different than antigenic drift, which refers to the natural mutation of a single strain of influenza
E. influenza; in contrast to antigenic drift, which refers to the natural mutation of a single strain of influenza
Key: A. 此题里面D选项different than先改为different from。而即便改为different from，也修饰不到Antigenic shift，因为太远了，需要在different from前面加上and is(其他错误暂不考虑)。
不过如果前面的成分比较短，不会引起歧义，这个同位语还是可以跳跃修饰的，比如这个例子：
According to surveys by the National Institute on Drug Abuse, about 20 percent of young adults used cocaine in 1979, doubling those reported in the 1977 survey.
(A) doubling those reported in the 1977 survey
(B) to double the number the 1977 survey reported
(C) twice those the 1977 survey reported
(D) twice as much as those reported in the 1977 survey
(E) twice the number reported in the 1977 survey
OA：E。其中twice跳跃used cocaine修饰20 percent of young adults.
5. as many可以当一个数目来用。但是如果连接twice这样的倍数，则后面要用as many as，做比较来用。
一、twice的用法：
twice as many…as; twice as much…as;
twice + n.(可以是代词，比如that); twice + what从句;
*：一个大家常误会的句子：
The farm has more than twice as many cows as it has pigs.: 农场有多于猪两倍多的牛的数量(农场牛的数量比猪的两倍还要多)。(很多人会误读为猪比牛多。)
解读方法：可以类比一下A has B twice as many as C这个比较句型也可以写为A has twice as many B as C. 所以句子的核心是A has B，即：The farm has cows.
详细解读：twice as …as中前一个as是副词，more than twice as修饰many;而as it has pigs中的as自然是个连词，所以后面跟的是一个adverbial clause(状语从句/副词从句)，而as…as句型比较特殊，后面的as要与前面as所修饰的内容相呼应，所以as it has pigs应该与前面as所修饰的对象many相呼应，即as it has pigs也是修饰了many。不管怎么说as it has pigs都不是核心成分。这样翻译过来就是农场有牛，相当于两倍多的猪。故，牛多猪少。
二、用动词表达倍数：
double/triple/quadruple/quintuple/sextuple ----》这些动词可以做形容词(double还能做adv, predeterminer)
sth. double sth.; sth. is doubled; sth. double(adj.);
几个永远错误的形式：
(1)produce double; a doubling of; produce a doubling
(2)as much as twice the apples(much与apples矛盾)(要改为twice as many apples as; sth. double sth.)
*：这几个动词可以用主动也可以用被动，但是不能和as搭配;(差不多记住这句话就可以)
三、…times(或数字) as + 形容词或副词+as;
四、sb. be + 百分数 + more likely (to do sth.) than to do sth.(前面的to do 能省，后面的不能省)
如：at least fifty percent less likely than those who are sedentary to die of a heart attack
五、表达倍数用“… times + more +adj.+than，… time as +adj.+as”都正确
六、三类表示倍数的形容词为：twofold, threefold, fourfold, tenfold等。以twofold为例，其意思为two times as much or as many of something。该类词为形容词，多用于构成形容词+名词的词组，如：a threefold increase in revenue，少用于比较两个事物之间的倍数关系。
七、章振邦语法中介绍的倍数表达法：
i. x times(twice) + the + n. (twice还能做determiner)
ii. x times adj. (比较形式) than
iii. x times as adj. as 注意里面的adj.要和前面的名词匹配
A do x times as adj. … x as B do
iv. x times + what 分句 (名词性从句相当于名词)
v. x-fold
vi. double, triple, quadruple, quintuple, sextuple