could vs can

Translation

〜できた / 〜できる / 〜かもしれない / 〜できる / 丁寧な依頼

Meaning

The fundamental difference between these two modal verbs lies in probability and politeness. 'Can' expresses present ability, general possibility, or direct permission, whereas 'could' is the past tense of 'can' but is also used for hypothetical situations, lower probability, and much more polite requests.

Examples

• 私は今泳ぐことができます。
  I can swim across this pool easily.
• 若い頃はもっと速く走れました。
  When I was younger, I could run much faster.