So Do I / Neither Do I: Additive Agreement

Additive agreement is how English speakers say "me too" or "me neither" without literally saying "me too" — by using a short structure built from so or neither/nor, an auxiliary verb, and the subject. It lets you agree with someone else's statement without repeating the whole sentence.

• A: I love coffee. B: So do I. (I love coffee too.)
• A: I don't like olives. B: Neither do I. (I don't like olives either.)

Both patterns rely on subject–auxiliary inversion: the auxiliary verb comes before the subject, exactly as it does in questions ("Do you like jazz?") and in negative-adverbial inversion ("Never have I seen…"). Here, though, the inverted word order is not forming a question — it is signalling agreement.

Agreeing with a Positive Statement: So + Auxiliary + Subject

To agree with something positive, use So followed by an auxiliary that matches the tense and form of the original sentence, then the subject.

Original statement	Agreement	Auxiliary used
I like jazz.	So do I.	do (present simple, no other auxiliary present)
She works in Berlin.	So does her brother.	does (3rd person present simple)
We arrived early.	So did they.	did (past simple, no other auxiliary present)
She's tired.	So am I.	am (matches "am/is/are")
They've finished.	So have we.	have (present perfect)
He can swim.	So can I.	can (modal verb)
I'll be there.	So will I.	will (future)

The rule for choosing the auxiliary is simple: if the original sentence already contains an auxiliary or modal verb (be, have, can, will, should, must, etc.), reuse that same verb. If the original sentence has no auxiliary — because it's a present simple or past simple main verb — insert do, does, or did to carry the inversion.

Agreeing with a Negative Statement: Neither/Nor + Auxiliary + Subject

To agree with something negative, use Neither or Nor followed by the matching auxiliary and the subject. The auxiliary itself stays in its positive form — the negative meaning is already carried by "neither/nor," so you never add "not" as well.

Original statement	Agreement	Auxiliary used
I don't like olives.	Neither do I. / Nor do I.	do
He doesn't drive.	Neither does she.	does
We didn't see the film.	Neither did they.	did
She hasn't finished.	Neither has he.	has
I'm not hungry.	Neither am I. / Neither is she.	am / is
He can't drive.	Neither can I.	can
They won't come.	Neither will we.	will

Neither and Nor are interchangeable in this pattern in modern English, though Neither is more common in everyday conversation and Nor can sound slightly more formal or literary.

Full Contrast: Positive vs. Negative Agreement

• A: I speak French. B: So do I.  |  A: I don't speak French. B: Neither do I.
• A: My sister is a teacher. B: So is mine.  |  A: My sister isn't a teacher. B: Neither is mine.
• A: We've been to Japan. B: So have we.  |  A: We haven't been to Japan. B: Neither have we.
• A: He can cook. B: So can I.  |  A: He can't cook. B: Neither can I.
• A: I'll help tomorrow. B: So will I.  |  A: I won't help tomorrow. B: Neither will I.

Informal Alternatives: "Me Too" and "Me Neither"

In casual spoken English, native speakers very often skip the inversion pattern entirely and just say "Me too" (to agree with a positive statement) or "Me neither" (to agree with a negative one). These are quick, informal reactions with no auxiliary and no inversion:

• A: I'm hungry. B: Me too.
• A: I don't smoke. B: Me neither.

"Me too" and "Me neither" are perfectly natural in conversation with friends, but they are considered too casual for formal writing, presentations or academic English. In those contexts, "So am I" and "Neither do I" are the appropriate, grammatically explicit forms.

A Different Structure: "I Think So" / "I Hope Not"

Don't confuse additive agreement with the unrelated pattern where so or not stands in for a whole clause after verbs like think, hope, guess, believe or expect. There is no inversion here, and the meaning is different — it's not "me too," it's "I believe that is true/not true":

• A: Is it going to rain? B: I think so. (= I think it is going to rain.)
• A: Will she be late? B: I hope not. (= I hope she will not be late.)
• A: Did they win? B: I guess so.

This "so/not" pattern replaces an entire idea as a pro-form; it does not agree with someone else's statement about themselves the way "So do I" or "Neither do I" does.

Common Mistakes

• Forgetting inversion: The auxiliary must come before the subject, not after.
  Wrong: Neither I do.
  Correct: Neither do I.
• Double negative with "neither": "Neither" already carries the negative meaning, so the auxiliary must stay positive.
  Wrong: Neither don't I.
  Correct: Neither do I.
• Wrong auxiliary choice: The auxiliary must match the verb form of the original sentence, not default to "do" every time.
  Wrong: She's tired. So do I.
  Correct: She's tired. So am I.
• Using "So" to agree with a negative statement: "So" always signals agreement with something positive.
  Wrong: I don't like olives. So do I.
  Correct: I don't like olives. Neither do I.
• Mixing up "so + auxiliary + subject" with "I think so": These are two unrelated structures with different word orders and different meanings; don't invert after "I think" or "I hope."

Practice Tips

• Drill both directions: Practise turning positive statements into "So + auxiliary + subject" and negative statements into "Neither + auxiliary + subject" until the inversion feels automatic.
• Say it out loud with a partner: One person makes true statements about themselves; the other agrees using the correct pattern, choosing between "So" and "Neither" based on whether the statement was positive or negative.
• Compare formal and informal: For each example, practise both the grammatical form ("So do I") and the casual spoken alternative ("Me too") so you can use the right register in the right situation.

Practice Exercises

Explore related grammar topics:

All Grammar Topics Inversion Auxiliary Verbs Ellipsis Tag Questions Word Order

Frequently Asked Questions

What is the rule for "So do I"?

"So do I" is used to agree with a positive statement someone else has made. The pattern is "So + auxiliary + subject," where the auxiliary must match the tense and form of the verb in the original sentence. If the original sentence has no auxiliary (present simple or past simple main verb), you insert "do," "does" or "did": "I like jazz." "So do I."

What is the rule for "Neither do I"?

"Neither do I" is used to agree with a negative statement. The pattern is "Neither/Nor + auxiliary + subject," with the auxiliary matching the original sentence but kept in its positive form, since "neither" already carries the negative meaning: "I don't like olives." "Neither do I." You can also say "Nor do I" with the same meaning.

Why do "So do I" and "Neither do I" use inverted word order?

Both patterns require subject-auxiliary inversion, the same mechanism used in questions and in negative-adverbial inversion, but here it signals agreement rather than a question. The auxiliary moves in front of the subject: "So am I," "Neither have we," "So can she." Saying "Neither I do" instead of "Neither do I" is a common learner error because it skips this inversion.

How do I choose the correct auxiliary for "So" or "Neither"?

Look at the auxiliary or modal verb already in the original sentence and reuse the same one: "be" gives "so am/is/are," "have" gives "so/neither have/has," modals like "can" or "will" stay the same. If the original sentence is present simple or past simple with no auxiliary, insert "do," "does" or "did" depending on the subject and tense: "She works in Berlin." "So does her brother."

What is the difference between "Neither" and "Nor" in this pattern?

"Neither" and "Nor" are largely interchangeable when agreeing with a negative statement: "Neither do I" and "Nor do I" mean exactly the same thing. "Neither" is more common in everyday spoken English, while "Nor" can sound slightly more formal or literary, but both require the same auxiliary-subject inversion.

What is the difference between "So do I" and "Me too"?

"So do I" is the grammatically explicit form, built with subject-auxiliary inversion, and is appropriate in both spoken and written/formal English. "Me too" is an informal spoken shortcut with no auxiliary and no inversion, used casually among friends but generally avoided in formal writing or professional contexts.

What is the difference between "Neither do I" and "Me neither"?

"Neither do I" is the standard grammatical structure using inversion, suitable for formal and informal contexts alike. "Me neither" is its casual spoken equivalent, used to quickly agree with a negative statement in conversation, e.g. "I don't smoke." "Me neither." It is not typically used in formal writing.

Is "I think so" related to "So do I"?

No, they are different structures. "I think so" uses "so" as a pro-form replacing an entire clause after verbs like think, hope, guess or believe, with no inversion: "Is it going to rain?" "I think so." (= I think it is going to rain.) "So do I" agrees with someone else's statement about themselves and always requires auxiliary-subject inversion. The two patterns should not be confused.

Why is "Neither don't I" incorrect?

"Neither don't I" is a double negative and is ungrammatical. "Neither" already expresses the negative meaning by itself, so the auxiliary that follows it must stay in its positive form: "Neither do I," not "Neither don't I." Adding "not" or "n't" as well creates a redundant double negative that native speakers do not use.

At what level are "So do I" and "Neither do I" typically taught?

This pattern is usually introduced at B1 level as a natural extension of auxiliary verbs and short answers, then reinforced at B2 alongside other subject-auxiliary inversion structures. Learners at B1/B2 are expected to use both "So + auxiliary + subject" and "Neither/Nor + auxiliary + subject" accurately in conversation and writing.