Uses of Can and Could Can To express ability Can is used to express present or general ability. I can swim. She can knit. We can speak English. Can you speak French? She can draw beautiful pictures. To give permission Can is sometimes used in the sense of may to give permission. Note that many people consider this usage incorrect and prefer using may. You can take one of those books. (More correct: You may take one of those books.) She can do whatever she wants. (More correct: She may do whatever she wants.) You can go now. (More correct: You may go now.) Now-a-days can is also being increasingly used to ask permission. While this practice is common grammarians still insist on using may for asking and giving permission. Can I come in, Sir? (More correct: May I come in, Sir?) Can I go to the pictures, Mom? (More correct: May I go to the pictures, Mom?) Could In indirect speech Could is the past tense form of can in indirect speech. Direct speech: She said, “I can’t climb up the hill.” Indirect speech: She said that she couldn’t climb up the hill. He said, “I can solve the problem.” He said that he could solve the problem. To talk about past ability Could is used to talk about ability that existed in the past. In my younger days I could run miles at a stretch. I could swim across that river when I was young. She could read when she was three. Why couldn’t you finish the work in time? Note that could refers to past time only when the context makes the time clear. To talk about possibility or uncertainty Could is used to talk about possibility or uncertainty. It is also common in conditional sentences. You could win, if you worked hard. (Possibility) She could pass if she studied hard. (Possibility) I could have helped him if he had asked me. If I had the money I could buy a car. In polite requests Could is often used in questions expressing polite requests. Could you wait for a minute? Could I lend your bicycle for a day? Could you, please, take me to the manager? Could I have a cup of coffee?

The reason that you have to say "can" instead of "could" is the following. In English, the conditional is usually formed as follows: would + infinitive for example: I would be happy. "Can" is a "defective verb". This means that it lacks certain conjugations. "Can" is defective and irregular. This leads to the simple past and the conditional of "can" being the same: "could". In practise, you can replace "could" with either "would be able to" or "was able to". If, in your sentence, one tries this, one gets: 1. I hope that you would be to help me. 2. I hope you were able to help me. Grammatically speaking, only the second is correct. But does not mean what you want to say. If one wants to use "be able to" in this instance, the correct options are: 1. "I hope you are able to help me." 2. "I hope you will be able to help me." Can is defective and therefore does not exist in the future tense, thus we use it in the present. It is because of this that you have to say "I hope you can help me."

I don't like either of them. If you want help ask, can you help me?please.(This means that the person is capable of helping you). Could you help me?(You are asking him, if he is capable.) I think this is correct but, do get it checked by a native speaker.