Learn English – Comparisons: “so [adjective/adverb] as” or “as [adjective/adverb] as”


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.

Best Answer

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.