[User 'Colin Fine' 's answer:] Note that so here [in so do I] has a different meaning from that it would have in the normal order ("I do so") - [the inverted so] means 'also', or 'as well' and it seems to me that it can have that meaning only when fronted. The fronting is clearly for emphasis, but that in itself is not enough to explain why the fronting is obligatory for that meaning.

So why's subject-auxiliary inversion necessary in such elliptical sentences? I doubt or don't understand the other answers in that question, such as this.

Footnote: Wikipedia doesn't appear to explain this necesary inversion.

  • Conjecture: this probably goes back to Old English swa do ic eac ["so do I also"] with swa in leading position to put emphasis on the "in like manner" element of the statement. [Old English was heavily inflected and did not operate by the word-order conventions as Modern English, in which the final word often gets the spotlight.] With time swa do ic became a collocation, the "eac" becoming unnecessary and dropping out, just as in the modern variant "I do too" the "so" is unnecessary.
    – TimR
    Commented Mar 2, 2015 at 11:28

2 Answers 2


Let's look at some examples that build up to the usage of "so do I" or "as do I".

  • Step 1: She likes apples. I like them too.
  • Step 2: She likes apples, just as I like apples.
  • Step 3: She likes apples, just as I do. (here 'do' is an auxiliary verb that plays the role of 'like apples').
  • Step 4: She likes apples, as do I. (here we see the inversion - you can think of it as idiomatic usage really. 'as' plays the role of 'just as' or 'just like')

We could've taken a slightly different sequence of steps:

  • Step 2: She likes apples, and I like apples too.
  • Step 3: She likes apples, and I do too. (again, 'do' here is in place of 'like apples')
  • Step 4: She likes apples, and so do I.

Here is the inversion again, and it is idiomatic again, but in this case think of so as the second half of (al)so. In fact the two words are related: also = all + so: http://www.etymonline.com/index.php?term=also


In German there is subject verb inversion whenever a sentence begins with something that is not subject. This kind of inversion is automatic in German.

English has in some cases kept this feature that goes back to old times. English uses this kind of inversion after negative or similar adverbs as

  • never, rarely, seldom (adverbs of frequency)

And some others

  • hardly/scarcely ... when - no sooner ... than - nor - in vain - little.

This is a feature of written language. In spoken language regular word order is preferred.

This inversion is also used in short reactions beginning with

  • so, nor/neither, no more as in

  • So do I - Nor/Neither am I -No more can I

I have never managed to get this grammar point into an optimal form, so it can be remembered easily. Furthermore it seems that writers can use this kind of inversion after other sentence introductions that are not subject. Such a grammar point is not worth much without a lot of example material, but I have not the time for it. It is recommendable to study this type of inversion in a larger grammar where you will find example sentences.

This grammar point is a subsection of a larger chapter "Inversion after adverbs".

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