Swam vs. Swum
“Swam” and “swum” are different forms of the irregular verb “swim.” “Swam” is the simple past, while “swum” is the past participle used in perfect constructions and, where applicable, passive constructions.
Use “swam” for the simple past and “swum” as the past participle, especially after have/has/had.
Key details
Choose the right form
| Grammar slot | Form | Decision |
|---|---|---|
| simple past without an auxiliary | swam | Use the past-tense form. |
| past participle after have/has/had | swum | Use the participle. |
| passive/perfect-style participial slot where the verb is grammatically a participle | swum | Do not substitute the simple-past form “swam.” |
Quick tests
Auxiliary test
Is the form after “have,” “has,” or “had”?
If yes: Use “swum.”
If no: For a simple past with no perfect auxiliary, use “swam.”
Caveat: This is a grammatical form distinction: the reviewed dictionary gives “swam” as past tense and “swum” as past participle.
Examples
She swam across the lake yesterday.
“Swam” is the simple-past form.
She has swum across the lake many times.
After “has,” the verb requires the past participle “swum.”
By noon, they had swum two kilometres.
After “had,” “swum” fills the participle slot.
Further guidance
Core difference
“Swam” is the simple-past form of “swim”; “swum” is the past participle used with auxiliaries such as have, has, or had and in passive constructions when the verb permits them.
Fast Test
If have, has, or had directly governs the form of “swim,” choose “swum.” For a standalone finite past-tense verb, choose “swam.”
Sources and evidence
Sources are shown with the role they play in this guide. Historical or style-sensitive claims are kept within the evidence boundary described above.
- Swim — Cambridge Dictionary (opens in a new tab)Cambridge University Press · Direct verb-form evidence: swim has past tense swam and past participle swum.