Past Tense of “do”
The past tense of do is did; the past participle is done.
Why “do” behaves this way
"Did" is one of the last visible traces in English of an ancient Germanic verb-formation process called reduplication, where the past tense was formed by repeating part of the verb's stem rather than by a vowel shift or a suffix. Old English "don" (do) formed its past tense "dyde" by reduplicating and then contracting, a pattern shared with the German cognate "tun/tat" (do/did). Almost every other reduplicating verb in the Germanic languages has since leveled out to a regular ablaut or weak pattern, which makes "do/did/done" a genuine linguistic fossil — one of the very few surviving reduplicated preterites in modern English.
"Do" is also unusual for how much grammatical work it does beyond its literal meaning: it's the "dummy auxiliary" that forms English questions ("Did you see that?") and negatives ("I did not see that"), a construction called "do-support" that didn't fully standardize in English until relatively late, around the 16th-17th centuries. Older English (and Shakespeare) could still form questions and negatives without "do" ("Saw you that?" "I saw it not"), a pattern modern English has almost entirely lost outside of fixed poetic phrasing.
The common confusion
The main real-world confusion isn't did vs. done in isolation, but using "done" where "did" belongs in casual speech ("I done my homework"), a nonstandard dialectal pattern rather than a spelling mix-up — "done" always needs a helping verb (have/has/had) attached in standard English, exactly like "gone" above.
How it's actually used
As one of only a few verbs that also functions as a grammatical auxiliary, "do" appears constantly in emphatic statements ("I did lock the door") and in tag questions ("You like it, don't you?"), uses that have nothing to do with its literal meaning of performing an action. Non-native speakers often over- or under-use do-support because their own languages handle questions and negation without any equivalent helper verb, making "do" one of the more genuinely difficult high-frequency verbs to internalize despite its simple-looking conjugation. "Do" also stands in for an entire preceding verb phrase to avoid repetition, a function grammarians call "verb phrase ellipsis": "She finished her homework before I did" avoids repeating "finished my homework," and "Does he like coffee? He does" avoids repeating "like coffee" — a compact substitution pattern that most other English verbs simply can't perform on their own.
Across the tense system
"Do" shows its full range across tenses mostly in its auxiliary role rather than as a main verb: "I do agree" (emphatic present), "I did warn you" (emphatic past), "Do you think so?" (question formation), "I don't think so" (negation) — in each case "do" carries no independent meaning of its own, purely grammatical scaffolding, which is different from its main-verb use in "I did the dishes."
Common real mistakes
"I done that already" for "I did that already" is one of the most common nonstandard past-tense errors in English, alongside the reverse error of using "did" after a helping verb ("I have did it" instead of "I have done it") — both stem from did/done being less intuitive than more everyday irregular pairs. A separate, purely orthographic error is writing "did" as "did'nt" or misplacing the apostrophe in "don't"/"doesn't" altogether, especially among learners whose first language doesn't use apostrophes for contraction at all; because "do" is so central to negation, these small punctuation slips show up constantly in early written English even from otherwise fluent speakers.
Examples
- I did my homework before dinner.
- She has done everything the manual asked.
- Have you done this before?
- They did well on the exam.
- We had done all we could by that point.
- He does the dishes every night.
- Do you understand the instructions?
- She doesn't usually work weekends.
Memory trick
Picture "done" as unable to stand on its own two feet — it always leans on "have," "has," or "had" for support, so a bare sentence needs "did" instead. And remember "do" moonlights as the invisible helper in questions and negatives ("did you go?"), a separate job from its role as a main verb.