a closed book

USAGE SUMMARY

"a closed book" is correct and usable in written English.
It is typically used as a metaphor for something that is difficult to understand or comprehend. For example, "Understanding quantum physics is a closed book to me."

✓ Grammatically correct

News & Media

Academia

Science

Human-verified examples from authoritative sources

Exact Expressions

54 human-written examples

Gita, too, was a closed book.

The Guardian - Books

His interpretations remain, for me and others, a closed book.

The New Yorker

I think that's pretty much a closed book for me".

Independent

History is never a closed book or a final verdict.

The New York Times

In 2007 he announced, "I think acting is pretty much a closed book to me".

The Guardian - Film

But the history presented in this film "hardly feels like a closed book or a museum display," he added.

The New York Times

Human-verified similar examples from authoritative sources

Similar Expressions

6 human-written examples

You mean after what happened with your mum? ‘Yeah, that’s just a... closed book, you know what I mean?’ He’s speaking in a terse whisper now.

The Guardian - Film

So right before the final, Professor Duneier detailed the rules for a closed-book exam, realizing that international students might not share American concepts of plagiarism.

The New York Times

Grading: Grades will be based solely on a closed-book final examination.

Duke University

Grades will be based solely on a closed-book final examination.

Duke University

This is a closed-book test.

Los Angeles Times

Expert writing Tips

Best practice

Use "a closed book" when you want to describe someone or something that is difficult to understand or know. For example, you can say "Her past is a closed book to me" to indicate you know nothing about her past.

Common error

Avoid using "a closed book" in literal contexts. It's a figurative expression, so don't use it to describe an actual, physical book that is simply closed.

Linguistic Context

The phrase "a closed book" functions as a metaphorical noun phrase, typically serving as a predicate nominative or object complement. It describes someone or something that is difficult to understand or know. Ludwig AI confirms its correct usage.

Expression frequency: Very common

Frequent in

News & Media

60%

Academia

20%

Science

10%

Less common in

Formal & Business

5%

Encyclopedias

3%

Wiki

2%

Ludwig's WRAP-UP

The idiom "a closed book" is a common and versatile phrase used to describe someone or something difficult to understand or know. Ludwig AI confirms that the phrase is correct and appropriate for use in written English. As evidenced by the numerous examples, it is frequently found in news and media, as well as academic and scientific contexts. When writing, ensure that you're using it figuratively, to describe abstract impenetrability, rather than literally. Related phrases like "an enigma" or "a mystery" can serve as alternatives depending on the specific nuance you aim to convey.

More alternative expressions

Phrases that express similar concepts, ordered by semantic similarity:

an enigma

Focuses on the mysterious and puzzling nature.

a mystery

Emphasizes the lack of understanding or knowledge about something.

inscrutable

Highlights the difficulty in interpreting someone's thoughts or feelings.

impenetrable

Stresses the inability to get through or understand something.

reticent

Describes someone who is unwilling to communicate freely.

guarded

Implies a cautious and secretive nature.

uncommunicative

Directly indicates a lack of communication.

secretive

Emphasizes the act of keeping things hidden.

difficult to fathom

Highlights the struggle to understand or comprehend.

beyond comprehension

Indicates that something is impossible to understand.

FAQs

How can I use "a closed book" in a sentence?

You can use "a closed book" to describe someone who doesn't reveal their thoughts or feelings, or a subject that is hard to understand. For example, "He's such a private person, he's like a closed book" or "Advanced calculus is a closed book to me".

What does it mean when someone is described as "a closed book"?

Describing someone as "a closed book" means they are difficult to know or understand because they don't easily share their thoughts and feelings. It suggests they are private and reserved.

What are some alternatives to saying "a closed book"?

You can use alternatives like "an enigma", "a mystery", or "inscrutable" depending on the specific context.

Is "a closed book" a formal or informal expression?

"A closed book" is generally considered an informal expression, although it can be used in neutral contexts as well. In very formal settings, you might prefer a more direct phrase like "difficult to understand" or "private and reserved".