1. I can swim well.
2. I could swim well.
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What is the difference between the two sentences?
Is 'could' politer than 'can' in meaning?
could is the past tense of can
I can swim well.
Yesterday I could swim well.
Then there are the conditional and perfect uses, but maybe you're not after those.
Steve is correct.
In addition, this webpage should have additional information you can use:
http://grammar.ccc.commnet.edu/grammar/auxiliary.htm#can
The difference between the two sentences lies in the verb tense being used.
1. "I can swim well" is in the present tense and indicates your ability to swim well in the present time. It implies that you have the skill and capability to swim well currently.
2. "I could swim well" is in the past tense and suggests that you had the ability to swim well in the past. It implies that you had this skill at a previous point in time, but it doesn't clarify whether you still possess the same level of ability.
Regarding the politeness, 'could' is sometimes considered more polite than 'can' when making a request or seeking permission. For example, instead of saying "Can you pass me the salt?", using "Could you pass me the salt?" may sound more polite. However, in the context of these sentences, politeness isn't a significant factor since they are simply statements about your swimming ability.