談談比較類句型里的一個現象

本文首發於立文悉通微信公眾號（Transystom）

關於比較類句型我們會發現這麼一個現象：有時在than後會有does或is，且看以下句子：

• The population studied has a substan tially lower risk of colon cancer than does the general US population.
• Moderately intense exercise carries a lower risk of musculoskeletal injuries and acute cardiovascular events than does intense exercise.
• Percutaneous drainage is associated with a lower risk of cholangitis than is use of a retrograde approach.

為什麼than後有does或is呢？

讓我們先看看WordReference論壇上的一個問題

https://forum.wordreference.com/threads/more-than-the-boys-or-more-than-did-the-boys.2948052/

埃及網友One Heart提出了一個問題：

The girls drank water more than (did) the boys.

Is did compulsory here? If it is optional, which do you prefer?

Thanks!

這和我們上面的問題一樣，在這裡did是必須的嗎？如果不是必須的，是加好還是不加好？

英國網友wandle回答得不錯，我們來看看：

First, let me confirm that this sentence compares how often the two groups drank water: it does not compare how much water they drank (that would be drank more water than).

樓上有些網友認為這句話應該寫成：The girls drank more water than (did) the boys.而不是The girls drank water more than (did) the boys.其實這兩句話從語法上來說都是沒有問題的，但是意思不一樣。

drank water more強調的是喝水的頻繁程度，比如是否經常喝水，而drank more water強調的是喝水的量，比如是喝了兩杯水還是一杯水。

For a sentence of this kind (comparing the activity of two groups) did is not wrong, but it is usually not needed.

在這句話中，使用did沒有錯，但並不是必須的。

It is better style to leave it out, unless it is needed to avoid ambiguity, or preserve another part of the sentence structure.

有兩種情況需要使用did：1）避免歧義；2）保持句子結構的平衡。

For example, The girls liked the cats more than the boys is ambiguous.

例如這句話：The girls liked the cats more than the boys，如果than後不加did的話就會引起歧義：到底是「女孩喜愛貓的程度要大於男孩喜愛貓的程度」還是「女孩對貓的喜愛程度大於女孩對男孩的喜愛程度」？

We can remove the ambiguity by saying "The girls liked the cats more than did the boys."

如果在than後加上did，那就很明確了：boys是like的主語（而非賓語），「女孩喜愛貓的程度要大於男孩喜愛貓的程度」。

However, even in this case, the more natural word order is more than the boys did.

Even so, there are occasions when you need to place did before the second subject, for the sake of the syntax, but a simple example like the topic sentence is not such an occasion.

不過在這個句子中，我們最好把did放在boys（第二個主語）後面，即：The girls liked the cats more than the boys did. 因為boys這個主語很短，只有一個單詞。

如果第二個主語比較長，那麼為了句子結構的平衡，就應該把did放在第二個主語的前面了，比如：The girls liked the cats more than did the boys, who usually liked the dogs.

than後的does、is的主要作用就是明確比較對象，避免歧義。

• 如果是兩個主語比較，就可以（但並不一定必須）用does、is：

ST use carries a lower risk of oral cancer than (does) continued smoking.

如果第二個主語比較長，就把does、is放在第二個主語的前面，如果第二個主語很短，就把does、is放在最後。

• 如果是兩個賓語比較，就不用does、is：

Cigarette smoking has shown a stronger association with risk of rectal cancer than colon cancer.

當然，很多時候我們並不需要藉助does、is來判斷比較的對象，回到最開始的那幾個句子，than後的does、is可以不加，因為我們可以從意思上判斷出比較的對象。

比如：

The population studied has a substantially lower risk of colon cancer than (does) the general US population.

去掉does後，雖然在語法上可以有兩種理解，但顯然是 the general US population和the population studied比較，我們不會認為是the general US population和colon cancer比較。