When learning how to make comparisons, students of English as a foreign language are first told to use the structure "as [adjective/adverb] as". However, at higher levels, they are told that both options ("as/so [adjective/adverb] as") are correct.

I've been wondering if there are any differences between them, but I can't find an answer in my grammar (Cambridge Grammar of English). In a school book, I saw two examples that led me to think that:

  1. "as [adverb] as" is possible with both positive and negative sentences
  2. "so [adverb] as" is only possible in negative sentences

Is this correct? If so, does it also apply to adjectives?

Examples for adjectives:

  • This is as good as that.
  • This is so good as that.

  • This isn't as good as that.

  • This isn't so good as that.

Examples for adverbs:

  • Anne plays as well as John.
  • Anne plays so well as John. (not correct?)

  • Anne doesn't play as well as John.

  • Anne doesn't play so well as John.
  • Could you possibly provide some examples of what you mean?
    – WS2
    Commented Nov 14, 2013 at 16:39
  • Is 'This is so good as that.' a grammatical sentence? You haven't added '(not correct?)' to the sentence, unlike in the case of the sentence 'Anne plays so well as John.', which contradicts your statement 'However, at higher levels, they are told that both options ("as/so [adjective/adverb] as") are correct.'. If you now understand the concept of 'as...as...' and 'so...as...', could you explain to me your reasoning? I myself am learning English and some explanations would be great.
    – user26486
    Commented Jun 25, 2014 at 18:55

2 Answers 2


Yes. So is an alternative to as in this construction in negative contexts, but not otherwise. I don't use it in my idiolect, but many people do.

  • "Anne doesn't play so well as John" sounds completely wrong to my British ears. It may be acceptable in other countries, but I would view this as grammatically incorrect.
    – mleonard
    Commented Sep 21, 2021 at 23:40

The rule as I learned it from an anecdote about Walter Lippmann's anger when a writer failed to follow it is this:

Use "as" in positive comparisons, "so" in negative comparisons.


  • I am as tall as she, but not so tall as he.
  • I am hardly so stingy as that, though I am as thrifty as one should be.
  • The cars today are not so fast as they once were.

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