Using Can and Could

Can and could are, like will and would, modal verbs (check out my post, "I Will Miss You, Pavarotti!" for more on these verbs). Just to remind you, modal verbs are auxiliary (helping) verbs that, when combined with the main verb of a sentence, add a mood or a tense to the verb. For example, "You can sing, right?" The modal is can and combined with the verb sing, communicates a mood which shows the ability of the person being referred to. Can and could, after all, are both modal verbs that communicate ability. So, we say, "She can play the piano," "Could you play the piano," "She could dance when she was a child."

Looking at the three examples, we can see the differences between can and could. Although both communicate ability, there are two differences between them. The first is, could is more polite, so it's best to use it when you're asking someone to do something for you: "Could you turn on the radio, please?" Although can is usable ("Can you turn on the radio, please"), could carries a more polite tone (it is necessary to be polite when asking someone to do something for you). The second difference is could is used as the past tense of can. Consider: "Today, she can only dance the flamenco, but when she was a child, she could also dance ballet."

I hope you all can do good work today!