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I am considering these two sentences:

  • I have no idea.
  • I have no ideas.

Are they both correct, and if so, are they synonymous?

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  • Franck, interestingly in a situation where yuou would say "I have no idea": you definitely would not say "I have no ideas". It would sound like "learning English" or "deliberate silly baby talk".
    – Fattie
    Aug 24, 2023 at 17:10
  • There's a difference in nuance: "I have no idea." = I really don't know. I have not even a single idea, no comprehension whatsoever. "I have no ideas." = I am all out of ideas. I can't make any suggestions. No original concepts come to mind for me regarding this topic.
    – Mentalist
    Aug 26, 2023 at 7:35

2 Answers 2

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They are both correct and they do not mean the same thing.

"I have no idea" means "I do not know the answer to your particular question." It is about a complete lack of knowledge. It is a counterpart to a less common phrase "I have an idea what the answer is", which is used before answering a question when you think you know what the answer might be, but you are not sure that you are correct.

"I have no ideas" means "I am not creative and I have no original thoughts." It can also have the related meaning, if you are asked to come up with something to do, that "I cannot think of anything to do."

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  • 33
    Thanks, I had no idea. Aug 24, 2023 at 4:14
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    Note: "I have no idea" is a very common, borderline idiomatic phrase, which might be said in casual conversation on any given day; whereas "I have no ideas" is not something a person would say very often. The latter would likely be used very situationally as a statement about a specific problem.
    – Brian Lacy
    Aug 24, 2023 at 16:45
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    @FranckDernoncourt emphasizing what Brian said. "I have no ideas" can only exist as an answer to an obscure question such as: "John, do you have any ideas for the new TV ad we are working on?" Even in that case it would be VERY unusual to answer "I have no ideas". You'd say something like "I've come up with no ideas so far".
    – Fattie
    Aug 24, 2023 at 17:32
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    @Fattie I can think of much less obscure questions, such as, WIFE: "Where can we go out to eat tonight that will make everybody happy?" HUSBAND: "I have no ideas."
    – ohwilleke
    Aug 24, 2023 at 19:32
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    My usual use of "I have no ideas" would be in the context of a "brain-storming" meeting, either about something technical or about something that needs immediate attention. "Did you see what Twitter is saying about our new product - gather the managers in the conference room and let's figure out what to do". Time passes, everyone is in the conference room, and the boss asks everyone, one-by-one, how to respond. When they get to me: "Sorry, I have no ideas".
    – Flydog57
    Aug 24, 2023 at 23:14
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To have no idea is a phrase or idiom–depending which reference you consult–whose meaning is easily found in most online dictionaries. It has in fact two different meanings.

  1. Cambridge Dictionary

have no idea

    phrase

(level) B1 informal to not know something:

  • "Where's Serge?" "I've no idea."
  • We had no idea when the power might come back on.
  • "What do you think Bonnie would like for her birthday?" "I have absolutely no idea."

Oxford Learners' Dictionaries

idiom
have no idea, not have the faintest, first, etc. idea (informal)
used to emphasize that you do not know something

     “What's she talking about?” “I have no idea.”
     He hasn't the faintest idea how to manage people.
     I had no idea she'd had such a difficult life.
     I don't have any idea where he is.

However…

  1. Merriam-Webster classifies it as an idiom, and offers two definitions
  1. to not know or understand
    I have no idea what you're talking about.
  2. —used to reply to someone as an emphatic "yes"
        "Was it hard?" "You have no idea (how hard it was)!"

Longman Dictionary concurs with the above and completely ignores the version with personal pronoun "I", and adds this detail

spoken used when you are telling someone that something is extremely good, bad etc

  • You have no idea how worried I was.

Collins Dictionary's definition implies that it is most commonly used with the second person singular

you have no idea/you've no idea (phrase)
You can say you have no idea to emphasize how good or bad something is. [informal, emphasis]

  • We are both so happy, you have no idea.
  • You have no idea how depressed it made me

While the meaning of “I have no idea”, in its uncountable sense, is similar to “I don't have a clue” and the Victorian-sounding “I haven't got the foggiest”; the second phrase “I have no ideas", with the stress on no, would suggest the speaker lacked the ability and imagination to create something original.

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  • I don't think the emphasis idiom can be used in the first person.
    – Barmar
    Aug 24, 2023 at 14:57
  • @Barmar Maybe for the second meaning the first person shouldn't be used in the present simple, but if it was in the past simple? "I had no idea what I was letting myself in for when I volunteered with a group of other mums and dads to look after 30 eight-year-olds in summer camp.“ P.S See the OP's comment which set off alarm bells in my head :)
    – Mari-Lou A
    Aug 24, 2023 at 15:03

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