"So + auxiliary + subject" expresses POSITIVE agreement ("me too / I do too"); "Neither/Nor + auxiliary + subject" expresses NEGATIVE agreement ("me neither / I don't either"). Both use INVERSION and the auxiliary must MATCH the tense of the original statement.
SO + AUXILIARY + SUBJECT: to express that the second speaker SHARES the same positive experience or condition. "I enjoy the new system." / "So do I." The structure inverts subject and auxiliary (like a question). The AUXILIARY must match the tense of the original statement: PRESENT SIMPLE -> SO DO/DOES I/he/she. "She reads a lot." / "So does he." PAST SIMPLE -> SO DID. "They visited the office." / "So did we." PRESENT PERFECT -> SO HAVE/HAS. "I have finished." / "So have they." BE -> SO AM/IS/ARE. "She is tired." / "So am I." HAVE (possessive) -> SO DO. "I have a car." / "So do I" (American English) or "So have I" (British, less common). COLLOQUIAL: "Me too" = informal equivalent of "So do I."
"Our team found the transition to the new project management platform significantly more intuitive than the previous system." / "So did ours — the onboarding curve was much shorter than we had anticipated."
"The regional director has already reviewed and approved the revised proposal." / "So has the chief financial officer — we received her sign-off early this morning."
"I am genuinely impressed by the depth of the market analysis in this report." / "So am I — it is considerably more thorough than what we typically receive from external research providers."
NEITHER/NOR + AUXILIARY + SUBJECT: to express that the second speaker SHARES the same NEGATIVE experience or condition. Used in response to NEGATIVE statements. "I do not enjoy the early meetings." / "Neither do I." NEITHER and NOR are interchangeable in this structure (NOR is slightly more formal). The auxiliary must match the tense of the original negative statement: NEGATIVE PRESENT SIMPLE -> NEITHER DO/DOES. "She doesn't like it." / "Neither does he." NEGATIVE PAST SIMPLE -> NEITHER DID. "They didn't attend." / "Neither did we." NEGATIVE BE -> NEITHER AM/IS/ARE. "I am not sure." / "Neither am I." NEGATIVE PRESENT PERFECT -> NEITHER HAVE/HAS. "I haven't seen it." / "Neither have they." COLLOQUIAL: "Me neither" or "Neither do I" = equivalents. "I don't either" = colloquial American alternative.
"The compliance team has not yet completed the third-party vendor assessment for this quarter." / "Neither has the risk management function — both teams are dealing with significant resource constraints."
"I don't believe the current proposal adequately addresses the scalability concerns raised in the technical review." / "Neither does the engineering lead — she has flagged the same issue in her written feedback."
"The organization was not adequately prepared for the pace of regulatory change in this sector." / "Nor were most of its competitors — the speed of the policy shift caught the entire industry off guard."
Common mistake
MOST COMMON ERRORS: (1) Wrong auxiliary. "I worked hard." / "So did I work hard" = INCORRECT. The response should only be "So did I" (without repeating the main verb). The structure is: SO + AUXILIARY + SUBJECT (nothing more). (2) Not inverting subject and auxiliary. "I have seen it." / "So I have." = INCORRECT. Correct: "So HAVE I" (inversion). (3) "So do I" in response to negative statements. "I don't enjoy it." / "So do I" = INCORRECT (implies you also do not-enjoy it in a strange way). Correct: "Neither do I." (4) "Neither I do" = INCORRECT (no inversion). Correct: "Neither DO I." (5) "Me too" in response to a negative: "I didn't like it." / "Me too" = technically incorrect but very common in colloquial English. The correct form is "Me neither" or "Neither did I."
Trick to remember it
THE MIRROR AUXILIARY RULE: the auxiliary in the response MUST BE THE SAME as in the original statement (or the one that would be used to form a question from that statement). "She is tired" -> question: "Is she tired?" -> auxiliary: IS -> response: "So AM I" (with first-person auxiliary). "They didn't come" -> question: "Did they come?" -> auxiliary: DID -> response: "Neither DID we." PROCESS: (1) Identify the auxiliary of the original statement. (2) If positive = SO + that auxiliary + subject. If negative = NEITHER/NOR + that auxiliary + subject. (3) INVERT: auxiliary goes BEFORE subject. "I work" -> DO + I -> "So DO I." "I am" -> AM + I -> "So AM I."
Quick rule
Positive: So + [aux] + subject (inversion). "I like it." / "So do I." Negative: Neither/Nor + [aux] + subject (inversion). "I don't like it." / "Neither do I." The auxiliary mirrors the tense of the original. Always invert. Colloquial: Me too (positive) / Me neither (negative).
Did you know?
The structures "so do I" and "neither do I" are examples of what linguists call CLAUSE ELLIPSIS — the omission of predictable parts of the clause to avoid repetition. "I enjoy it, and so does she" = instead of "I enjoy it, and she enjoys it too." Ellipsis with inversion (SO + inversion, NEITHER + inversion) is characteristic of English: other languages express the same concept in very different ways. Spanish uses "yo también" / "yo tampoco" (without inversion). German uses "ich auch" / "ich auch nicht." English is especially notable for using GRAMMATICAL INVERSION as an agreement-marking mechanism — the position of the auxiliary before the subject signals that this is an agreement response, not an independent declaration. This use of inversion as a pragmatic marker is one of the peculiarities of English that learners take longest to internalize.
Exercise 1 · Pick the right one
"The procurement director has already signed off on the revised vendor contract." / "_____ the chief legal officer — she confirmed her approval in this morning's email."
Exercise 2 · Pick the right one
"I do not feel that the current risk mitigation strategy adequately accounts for the systemic interdependencies between the three business units." / "_____ the risk committee — they raised the same concern in last quarter's review."
Exercise 3 · Form the word
Positive: So + [aux] + subject (inversion). "I like it." / "So do I." Negative: Neither/Nor + [aux] + subject (inversion). "I don't like it." / "Neither do I." The auxiliary mirrors the tense of the original. Always invert. Colloquial: Me too (positive) / Me neither (negative).
MOST COMMON ERRORS: (1) Wrong auxiliary. "I worked hard." / "So did I work hard" = INCORRECT. The response should only be "So did I" (without repeating the main verb). The structure is: SO + AUXILIARY + SUBJECT (nothing more). (2) Not inverting subject and auxiliary. "I have seen it." / "So I have." = INCORRECT. Correct: "So HAVE I" (inversion). (3) "So do I" in response to negative statements. "I don't enjoy it." / "So do I" = INCORRECT (implies you also do not-enjoy it in a strange way). Correct: "Neither do I." (4) "Neither I do" = INCORRECT (no inversion). Correct: "Neither DO I." (5) "Me too" in response to a negative: "I didn't like it." / "Me too" = technically incorrect but very common in colloquial English. The correct form is "Me neither" or "Neither did I."
THE MIRROR AUXILIARY RULE: the auxiliary in the response MUST BE THE SAME as in the original statement (or the one that would be used to form a question from that statement). "She is tired" -> question: "Is she tired?" -> auxiliary: IS -> response: "So AM I" (with first-person auxiliary). "They didn't come" -> question: "Did they come?" -> auxiliary: DID -> response: "Neither DID we." PROCESS: (1) Identify the auxiliary of the original statement. (2) If positive = SO + that auxiliary + subject. If negative = NEITHER/NOR + that auxiliary + subject. (3) INVERT: auxiliary goes BEFORE subject. "I work" -> DO + I -> "So DO I." "I am" -> AM + I -> "So AM I."
Bryan López
Founder of SpeakUP Academy