What is the past praticiple of can?

The past participle of "can" is could. However, "can" is a modal auxiliary verb, and it doesn't typically function as a past participle in the same way that a regular verb does.

Here's how "can" and "could" work:

* Can: Expresses ability or possibility in the present tense.

* Example: "I can swim."

* Could: Expresses ability or possibility in the past tense or as a polite request.

* Example: "I could swim when I was younger." or "Could you please pass the salt?"

While "could" is the past participle of "can," it doesn't often appear in a sentence structure that would normally use a past participle (like with "have" or "be").