What the pro-verb do does
In She works here, and I do too, work here is not repeated after do. Teaching descriptions often call this predicate substitution; syntactic analysis also describes this short auxiliary do as supporting ellipsis. What matters is understanding which meaning is recovered.
Compare this with it replacing a noun phrase: instead of “I bought a new laptop yesterday, and I'm happy with the new laptop”, we say “…and I'm happy with it”. Do serves a similar purpose for a verb phrase: instead of repeating the whole predicate, we use a form of do.
Do substitution often occurs with fronted so and subject–verb inversion: “My colleague finished early, and so did I” means the same as “…and I did too”. Both forms are used and natural.
Maria checks her email every morning before breakfast, and her assistant does too.
Maria checks her email every morning before breakfast, and her assistant does too.
Does stands for “checks her email every morning before breakfast”: the whole phrase, not just the verb.
The committee promised to review the proposal, and they did within a week.
The committee promised to review the proposal, and they did within a week.
Did stands for “reviewed the proposal”, the past form of the same predicate.
Noah left the office before six yesterday, and so did his manager.
Noah left the office before six yesterday, and so did his manager.
So did his manager uses fronted so with inversion; it means the same as “his manager did too”.
How much do replaces
A verb phrase is recovered, but not necessarily every adverbial from the original sentence. The new part can have a different time or place: She called on Monday, and I did on Tuesday.
Do not add an object again when it is already included in the recovered meaning: choose did so or did it instead of did so it. Additional adverbials and the full emphatic pattern did + base verb are possible, however; these are other grammatical patterns.
Liam finished sorting the archive faster than his colleague did.
Liam finished sorting the archive faster than his colleague did.
Did = “finished sorting the archive”; there is no need to add sorting the archive again after did.
I offered to proofread the article, and Nora offered to do the same.
I offered to proofread the article, and Nora offered to do the same.
Do the same is another way to refer to the whole action without repeating proofread the article.
Forms: bare do/does/did, done, doing, to do
The pro-verb changes form just like ordinary do: its tense form (do/does/did) agrees with the time and person it refers to, rather than mechanically copying the antecedent's form.
After have/has/had, use done; after a modal, use the base form do. With a to-infinitive, the safest options are to alone or to do so / to do it / to do that. Bare to do as a substitute is not equally natural in every variety and context.
Modal in the formula means a modal verb, such as can, will or should. The dots separate alternative patterns; this is not one long sentence.
do / does / did · have + done · modal + do · to / to do so / to do it / to do that
- modal —
- A modal verb expresses meanings such as ability, possibility or necessity: can, may, must.
She hasn't submitted her report yet, but I have already done it.
She hasn't submitted her report yet, but I have already done it.
After have, use done, not did.
You don't have to reply today, but you can do it whenever it suits you.
You don't have to reply today, but you can do it whenever it suits you.
After can, use the base form do, not does or did.
He wasn't required to test the module, but the lead asked him to do so before release.
He wasn't required to test the module, but the lead asked him to do so before release.
The infinitive to do so follows asked him; simply asked him to, without do, would also be natural.
The register scale: do so / do / do it / do that
Do, do so, do it and do that often convey related meanings, but register is not their only difference. Do so normally refers to an action or event; auxiliary do with ellipsis can also recover a state: She knows him, and I do too.
Do so is the most formal option, typical of reports, instructions and official texts. Bare do is neutral and natural in most contexts, including comparisons (than he does). Do it and do that are more conversational: they refer to an action as a specific thing already mentioned and sound natural in an everyday reply.
Check the particular sentence. Do not automatically add so to every short auxiliary: with know in the example, ordinary I do too does not require do so. Several alternatives may be acceptable when their structure and meaning fit the context.
Employees must report any safety incident within 24 hours; failure to do so may result in disciplinary action.
Employees must report any safety incident within 24 hours; failure to do so may result in disciplinary action.
Do so fits the official, written tone.
"Can you water the plants while I'm away?" "Sure, I'll do it."
“Can you water the plants while I'm away?” “Sure, I'll do it.”
Do it fits the conversational reply and refers to the specific action just mentioned.
Do after another auxiliary: British and American usage
When another auxiliary or modal verb already comes before do (have, will, might, should…), British English often adds do: I have done, I might do, I should have done.
In American English, this additional do is usually omitted, leaving the sentence to end with the auxiliary itself: I have, I might, I should have. Both alternatives are grammatically correct; this is a dialect difference, not an error in one of them.
Aux + do is characteristic of many British uses, but British English also allows the auxiliary alone. The label “British variant” does not mean that do must be added to every answer.
"Have you called the landlord about the leak?" "I have done, yes — this morning."
“Have you called the landlord about the leak?” “I have done, yes — this morning.”
The British variant: have + done.
"Have you called the landlord about the leak?" "I have, yes — this morning."
“Have you called the landlord about the leak?” “I have, yes — this morning.”
The variant without additional done is natural in both American and British English.
Preserve the action and set the new context correctly
The preceding text provides a basis for recovering an action or state. The new subject can be different, and some pronouns can change their reference: She washed her hands, and I did too usually means that each person washed their own hands. Do not require every participant to match literally.
Tense and person agree with the new subject and the time of speaking rather than being copied mechanically: if the antecedent is in the Past Simple and the new action is also in the past, use did; if you mean another person's present habit, use do or does according to the subject.
If the first sentence is negative and the second affirmative, or vice versa, do does not change polarity by itself: negation or its absence must be marked separately (didn't do so, doesn't do it).
Elena didn't attend the last two meetings, and her deputy didn't either.
Elena didn't attend the last two meetings, and her deputy didn't either.
Both parts are negative because neither person attended the meetings. With a different meaning, the contrast didn't … but … did is possible.
Our team hit the quarterly target, just as the design team did last quarter.
Our team hit the quarterly target, just as the design team did last quarter.
Did agrees with the past time of the second event; it does not copy the antecedent's form.
Distinguishing this from do in questions and negatives
Auxiliary do forms questions, negatives and emphasis: Does she work here? I don't agree. I do agree. In short answers, it can remain without a repeated verb: Yes, she does.
Word order therefore does not tell you whether this is substitution or an auxiliary: both Did she? after a preceding statement and so did I are possible. Distinguish a full verb following do from an unspoken predicate recovered from context.
Does he manage the warehouse? — Yes, he does.
Does he manage the warehouse? — Yes, he does.
In the question, does accompanies manage. In the short answer, does remains and manage the warehouse is not repeated.
She travels for work more than her manager does.
She travels for work more than her manager does.
Does is a pro-verb here in ordinary word order (manager does), not an inverted question.
Distinguishing this from clausal so/not (think so, hope not)
Do substitution replaces a verb phrase or predicate: “performed this action”. Clausal substitution is a different phenomenon: so or not, without do, replaces a whole idea or statement after verbs such as think, hope, believe or guess: “I think so”, “I hope not”.
The distinction is easy to check: if you remove so and leave only do in think so, the expression no longer works; do cannot function like that after think. Conversely, this verbal construction do so cannot be shortened to so alone: “did so” cannot be replaced by “so” without do.
"Will the results arrive today?" "I believe so."
“Will the results arrive today?” “I believe so.”
So replaces the whole clause “the results will arrive today” after believe; this is a related phenomenon, not do substitution.
They asked her to double-check the figures, and she did so before lunch.
They asked her to double-check the figures, and she did so before lunch.
Did so replaces the verb phrase “double-check the figures”; so cannot stand without do here.
When each form is natural
In comparisons (than, as) and after coordinating conjunctions (and, but), bare do/does/did is usually enough; it sounds neutral in any register.
In business correspondence, instructions, legal and academic texts, do so contributes to a formal tone, especially after expressions such as failure to, in order to and be required to.
In conversation, do it and do that sound more natural when one person has just named a specific action and the other agrees, refuses or confirms it; do that can add a slight sense of distance or surprise (“You actually did that?”).
Aux + do often occurs in conversational British English. In writing, the choice depends on the genre and the particular sentence; do not automatically cross this form out just because the register is formal.
"Would you consider relocating for this role?" "I might do, if the offer is right."
“Would you consider relocating for this role?” “I might do, if the offer is right.”
A conversational British reply with aux + do.
Common mistakes
Incorrect:He asked me to email the invoice, and I so immediately.
Correct:He asked me to email the invoice, and I did so immediately.
So alone cannot replace the verb phrase here. Unlike clausal so after think/hope (“I think so”), this construction needs do as its head: “did so”, not bare “so”.
Incorrect:They asked us to submit the form, and we did so it right away.
Correct:They asked us to submit the form, and we did it right away.
So, it and that are alternative complements to do, not complements that can be combined with each other; choose exactly one, rather than combining two in a single construction.
Incorrect:He promised to call, but he hasn't did.
Correct:He promised to call, but he hasn't done it.
After have/has/had, the pro-verb takes the past-participle form done, like any other verb after a perfect auxiliary; did is a simple-past form and is not used after have.
Incorrect:I haven't finished the report yet, but I will did tomorrow.
Correct:I haven't finished the report yet, but I will do it tomorrow.
After the modal will, the pro-verb remains in the base form do; did is already a finite past-tense form and cannot follow a modal verb.
Incorrect:He earns more than I did earned last year.
Correct:He earns more than I did last year.
Do not use earned after auxiliary did. Either short did with a recovered predicate or emphatic did earn is possible; the latter is grammatically correct in itself.
Incorrect:She forgot her keys yesterday, and I did forgot them too.
Correct:She forgot her keys yesterday, and I did too.
After auxiliary did, use the base form forget or ellipsis without repeating the verb. Did forgot incorrectly combines two past forms.
Incorrect:The company promised to fix the bug, and they made that within a week.
Correct:The company promised to fix the bug, and they did that within a week.
The pro-verb replacing an already named action is do (do it / do that / do so), not make: make names a separate action meaning “produce” or “cause” and does not serve as a general substitute for the preceding predicate.
Incorrect:He works from home most days, and his sister do too.
Correct:He works from home most days, and his sister does too.
In the present tense, the pro-verb agrees with the subject just like an ordinary verb: a third-person singular subject (his sister) requires does, not do.