The Economist上有一个有关GMAT的博客 -- GMAT Tutor Blog, 其中有一篇文章讨论了like和as的使用:



以下为文章原文节选, 加粗等标记还有中文补充是我后加的:

Most people hear and use the word “like” more pervasively than many other words in the English language. When it comes to the GMAT (sentence correction, in particular), the difference between like and as in a sentence is subtle enough to make it difficult to complete an otherwise straightforward sentence.

However, there isn’t quite as complicated a strategy to decide between these two words as you might be thinking. In fact, understanding the differences only requires a more intimate understanding of what type of word each one is. To help you tackle the tricky decision between like and as, we’ll actually take a step back and review the differences between a preposition and a conjunction.



English Vocabulary in Use 一书中提到认识一个单词，不仅要知道这个词什么意思，还要注意这个词能怎么搭配使用，和这个词有关的词有什么，这个单词的语法特点是什么 -- 词性(part of speech)还有具体的用法。很多时候我们用错一个词，就是因为我们忽略了它最基本的特征，才想当然的使用。例如like和as在某些句子中的用法区别，就是词性的不同 -- 一个是preposition, 一个是conjunction



The difference between a preposition and a conjunction

Choosing between like and as on a sentence correction question becomes much easier when you understand the difference between a preposition and a conjunction. You’ll see in the definitions of each below that while they are not too different in nature, the subtle differences between both will point you towards the right answer choice on test day.

• A preposition is a word that positions words in relation to one another, typically used when the following word is not a verb. Like would fall into this category, as well as words like “in,” “around” and “through.”
  
  

• A conjunctionis a more simple connecting word— it can connect everything from full sentences to individual words and does not itself define the relationship between the two items it connects (which prepositions such as ‘around’, ‘above’, and ‘like’ do). Other conjunctions include ‘and’, ‘but’, 'so,’ etc.
  
  

更具体的解释和使用请访问原文:

https://gmat.economist.com/blog/verbal/vs-do-you-know-difference-between-two





今天和大家分享的是在比较句中，than后面用主格还是用宾格, 例如这样一个句子:

Eric is taller than I am.



你或许见过以下两个版本:

1. Eric is taller than I.

2. Eric is taller than me.



简单的说，这两个版本都是正确的，主要的区别是than这个词到底是conjunction(如1), 还是preposition(如2)? -- 这个争论已经持续了几百年！我一直推荐的Grammar Girl在其博客回答了这个问题，原文请点击阅读原文阅读, 在此只是节选。

So the battle continues: the conjunctionists have history and the avoidance of ambiguity on their side, while the prepositionists have than whom and several counterexamples on theirs. Who wins? I believe Ken Wilson sums it up best in The Columbia Guide to Standard American English (3):

Than is both a subordinating conjunction, as in She is wiser than I am, and a preposition, as in She is wiser than me.... Since the following verb am is often dropped or “understood,” we regularly hear than I and than me. Some commentators believe that the conjunction is currently more frequent than the preposition, but both are unquestionably Standard.

So remember, than he and than him are both defensible, but not all grammar mavens feel this way. Therefore, I would avoid the prepositional use in formal settings, such as a research paper or job interview—and I would argue, advertising, but Cadbury obviously feels otherwise. The usage note in The American Heritage Dictionary (4) agrees: “The writer who risks a sentence like Mary is taller than him in formal writing must be prepared to defend the usage against objections of critics.” Unfortunately, defending your grammar during an interview is not the best way to make a good impression.

The quick and dirty tip to determining which pronoun is appropriate after the conjunction than is to figure out the pronoun’s role in the implied sentence by mentally filling in the missing words. Are you trying to say Aardvark likes Squiggly more than I [like Squiggly] or Aardvark likes Squiggly more than [Aardvark likes] me? Sometimes, even if you use the correct pronoun, you may find sentences like I'm taller than he sound too formal in casual setting. If so, you can use a verb to complete the implied sentence, saying instead, I'm taller than he is. With a verb present, the choice is obvious: subject pronouns are the only option. After all, both sides of the than he/than him debate agree that No bunny knows Easter better than he does.

另一篇文章里也提到了使用than me容易产生的ambiguity，以及than whom的用法:



一个万全之策就是把话说完整 -- "The safest option is to expand the words after than. This usually means adding at least the verb (e.g., than he is / than they have). This removes all ambiguity and stops your wording sounding pretentious." 例如上面的例句可以写为John likes Peter more than I do.

把这篇文章中提到的链接都看一遍，应该就清楚了。不懂得问题就多搜一搜, 注意参考内容是否具有一定的权威性, 要有基本的辨别和筛选能力，这种能力就是在一次一次的“探索”中提高的。