Swam vs. Swum: Who's Afraid of Irregular Verbs?

Carmella writes:

Hi Snarky! My Language Arts teacher is giving extra credit to anyone who can spot a grammar mistake in the news, and I think I've got one. In the San Diego Union-Tribune, there is a story about a man who swam in a local Gatorman race.  

In the fourth paragraph, it says 'he has swam'. I think that's an error. Shouldn't it be 'he has swum'?
 

Mighty impressive, Carmella! You're absolutely right. Many people will insist that there is no such word as swum, but they are wrong.

Swim, swam, swum is similar to shrink, shrank, shrunk; begin, began, begun; drink, drank, drunk; sink, sank, sunk; and a handful of other irregular verbs.

Swum is a participle used in the present perfect and past perfect tenses, to emphasize that an event has either recently been completed (present perfect, with 'have') or completed in the distant past (past perfect, with 'had').

Quick rules:

• Swim is used in the present tense. I swim slower than Michael Phelps.
• Swam is used in the simple past tense. Michael Phelps swam faster than everyone else. [Never: Michael Phelps swum faster than everyone else.]
• Swum is used in the present perfect and past perfect tenses and must be preceded by 'has', 'have', or 'had'. Michael Phelps has just swum in his last Olympics race. [In the present perfect tense, the signal word 'just' tells us that the event happened in the very recent past.]

Correction:

• Kostich, who said he has swum this race “15 or 16 times, I think,” used some furious freestyle stroking at the end of the popular open-water event to beat Tommy Anderson of Jamul by 18 seconds, in one of the closest races in recent history.