Example sentence
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Can you say that again?
もう1度言ってくれませんか。
English grammatical rules
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01 Possibility： We use the modal can to make general statements about what is possible:
- It can be very cold in winter.
- (= It is sometimes very cold in winter)
- You can easily lose your way in the dark.
- (= People often lose their way in the dark)
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We use could as the past tense of can:
- It could be very cold in winter.
- (=Sometimes it was very cold in winter.)
- You could lose your way in the dark.
- (=People often lost their way in the dark)
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We use could to show that something is possible
in the future, but not certain:
- If we don’t hurry we could be late.
- (=Perhaps/Maybe we will be late)
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We use could have to show that something is/was possible
now or at some time in the past:
- It’s ten o’clock. They could have arrived now.
- They could have arrived hours ago.
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02 Impossibility: We use the negative can’t or cannot to show that something is impossible:
- That can’t be true.
- You cannot be serious.
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We use couldn’t/could not to talk about the past:
- We knew it could not be true.
- He was obviously joking. He could not be serious.
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03 Ability: We use can to talk about someone’s skill or general abilities:
- She can speak several languages.
- He can swim like a fish.
- They can’t dance very well.
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We use can to talk about the ability to do something
at a given time in the present or future:
- You can make a lot of money if you are lucky.
- Help. I can’t breathe.
- They can run but they can’t hide.
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We use could to talk about past time:
- She could speak several languages.
- They couldn’t dance very well.
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04 Permission: We use can to ask for permission to do something:
- Can I ask a question, please?
- Can we go home now?
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could is more formal and polite than can:
- Could I ask a question please?
- Could we go home now?
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We use can to give permission:
- You can go home now if you like.
- You can borrow my pen if you like.
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We use can to say that someone has permission to do something:
- We can go out whenever we want.
- Students can travel free.
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Some people, however, think that may is more correct than can.
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- Can I go to the movies, mom? No, you can't.
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05 Instructions and requests: We use could you and as a polite way of telling or asking someone to do something:
- Could you take a message please?
- Could I have my bill please?
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can is less polite:
- Can you take a message please?
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06 Offers and invitations:We use can I … to make offers:
- Can I help you?
- Can I do that for you?
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We sometimes say I can ... or I could ... to make an offer:
- I can do that for you if you like.
- I can give you a lift to the station.
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日本語解説
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can、couldは一般に
- 能力
- 可能性
- 許可
couldはcanの過去形ですが、
直説法と仮定法に用いられます。
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- “Can he speak both English and French?”
- “Well, he can speak English fluently, but he can’t speak French very well.”
- 「彼は英語とフランス語が話せるのですか」
- 「そうですね、英語はペラペラですが、フランス語はそれほどでもありませんね」
[注] この意味のcan、cannotの未来形と完了形には
be able to、be unable to (＝not able to) を代用します。
- He will be able to succeed wherever he goes.
- （彼はどこに行っても成功することができるだろう）
- He has been unable to get a good job because of his poor health.
- （彼は体が弱くて、今までよい職につくことができなかった）
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mayのかわりにcanを用いて「許可」を表すことができます。
ただしこれはくだけた口語体の場合で、
それ以外はさけたほうがよいとも言われています。
なおこの用法で許可を求めるにはCan I～? を、
不許可にはNo, you can’t. を用います。
- You can go on holiday as soon as you like.
- （好きな時にはいつでも休暇をとっていいですよ）
- Can I speak to you a moment?
- （ちょっとお話してもよいでしょうか）
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否定文・疑問文において、
「～のはずがない」「よもや～だろうか」と否定的な推定や強い疑念を表します。
なお、過去の事柄に対して否定的推定を述べる場合には
「can (not) have ＋ 過去分詞」の形を用います。
- “Can it be true?” “No, it cannot be true.”
- 「一体それは本当だろうか」「いや、本当であるはずはない」
- I cannot have spoken ill of him; it must have been somebody else who said it.
- （ 私が彼のことを悪く言ったはずはない。言ったのはだれかほかの人にちがいない）
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「Can you ～ ?」のように
can を疑問文で使って
「～してくれますか」と依頼する表現ができます。
答え方は「～できますか」の場合と違って、
Yes, I can. や No, I can't. だけでなく、
- 快諾する表現、
- 渋る表現、
- 理由をつけて断る表現
など、バリエーションが豊富です。
- Can you help me with my homework?
- 宿題を手伝ってくれますか。
- No way.
- だめだよ。
- Can you pass me the salt?
- 塩をとってくれますか。
- Here you are.
- はい、どうぞ。
- Can you help me lift this box?
- この箱を持ち上げるのを手伝ってくれる？
- Can you take a message for your father?
- （電話で）お父さんに伝言をお願いできますか。
- Can you give me some advice about buying a house?
- 家の購入について何かアドバイスをしてくれませんか。
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- “Could you do it yourself?”
- “I’m sorry, I couldn’t.”
- 「自分でやったのですか」
- 「残念ながらできませんでした」
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should、wouldと同様に、
間接話法において主節の動詞が過去のときは、
時制の一致の原則により、canのかわりにcouldを用います。
- He said that he could not work together with us on the new designs.
- （＝He said, “I cannot work together with us on the new designs.”）
- 彼は新しい設計作業には協力できないと言った
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現在・過去の能力に反したことを仮想する場合で、
現在では「could ＋ 原形動詞」、
過去では「could have ＋ 過去分詞」の形を用います。
- If I could (＝were able to) do it, I would〔should〕be so happy.
- 今私にできることがあればとてもうれしいのですが
- If I had sold the shares〔stocks〕last week, I could have realized
- (＝should have been able to realize) a good profit.
- 先週持株を売り払っていたら、大もうけができただろうに
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canのかわりにcouldを用いると、
より丁重な要求や
さらに強い疑惑、あるいは
一層控え目な可能性
を表すことができます。
- Could you kindly spare me a few minutes?
- 2・3分時間をさいていただけませんか
- Please could I have your address and telephone number?
- 恐れいりますが住所と電話番号をおしえて頂けませんか
- Could it be true?
- それはほんとうでしょうか
- I could not act as chairman.
- 私には議長などはとてもつとまりません
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