a red flag

USAGE SUMMARY

"a red flag" is a correct and usable phrase in written English.
It can be used to describe a warning sign or a sign that there could be a problem. For example: - The politician's sketchy financial history was a red flag for many voters. - His constant excuses for being late were a red flag for his boss. - The doctor told me that any signs of dizziness or extreme fatigue could be a red flag for a serious underlying condition.

✓ Grammatically correct

News & Media

Formal & Business

Academia

Science

Human-verified examples from authoritative sources

Exact Expressions

60 human-written examples

"It's a red flag".

The New York Times

would be a red flag.

Massachusetts Institute of Technology

"It is sort of a red flag".

The New York Times

"That is a red flag," he said.

The New York Times

A mere blip, or a red flag?

The New York Times - Sports

"This raised a red flag," he said.

The New York Times - Health

Seems like a red flag.

The New Yorker

"Normally, that's a red flag," Nanis said.

The New Yorker

What might have raised a red flag?

The New York Times

He is waving a red flag.

The Guardian

But cost is still a red flag.

The Guardian

Expert writing Tips

Best practice

In formal business reports, pair the phrase with analytical verbs such as "identify", "constitute" or "represent" to maintain a professional tone.

Common error

Do not confuse "a red flag" with a "red herring". While a red flag is a legitimate warning sign of a problem, a "red herring" is a distraction intended to mislead or divert attention from the real issue.

Linguistic Context

The phrase "a red flag" functions as a noun phrase typically used as a subject complement or direct object. In the sentences provided by Ludwig, it frequently follows linking verbs (e.g., "is", "was") or acts as the object of active verbs like "raise", "throw up" or "constitute". Ludwig AI confirms its status as a correct and highly usable idiom in English.

Expression frequency: Very common

Frequent in

News & Media

55%

Formal & Business

30%

Academia

10%

Less common in

Science

3%

Social Media

1%

Wiki

1%

Ludwig's WRAP-UP

In conclusion, "a red flag" is a powerful linguistic tool used to denote a warning or a sign of danger. According to Ludwig, the phrase is ubiquitous in authoritative English, appearing in contexts ranging from relationship advice in The New Yorker to financial warnings in Forbes. It is most effective when used to describe early indicators of trouble. Ludwig AI highlights its grammatical correctness and versatility, making it a safe and evocative choice for writers seeking to convey alertness or skepticism. Remember to use it to identify genuine signs of concern and avoid confusing it with distractions like a "red herring".

More alternative expressions

Phrases that express similar concepts, ordered by semantic similarity:

a warning sign

Uses more literal language rather than idiomatic imagery

an alarm bell

Shifts the metaphor from visual to auditory signaling urgency

a cause for concern

Specifies the emotional or analytical reaction to the sign

a red light

Implies a need to stop immediately rather than just being a warning

a telltale sign

Focuses on the revealing nature of the evidence

a symptom

Often used in medical or systemic contexts to denote an underlying issue

a cautionary signal

More technical and formal than the standard idiom

a harbinger

Adds a literary or dramatic tone suggesting something major is coming

a deal breaker

Specifically refers to a warning that ends a negotiation or relationship

an omen

Introduces a sense of fate or superstition to the warning

FAQs

How do I use "a red flag" in a sentence?

You can use it to identify a problematic symptom, such as "The lack of transparency in the contract was "a red flag" for the investors."

What is the difference between "a red flag" and "a warning sign"?

Both terms are nearly interchangeable, but "a red flag" is more idiomatic and often implies an intuitive or systemic alert, whereas a "warning sign" can be more literal.

What can I say instead of "a red flag"?

You can use alternatives like "a cause for concern", "an alarm bell" or "a telltale sign" depending on the context.

Can I use "a red flag" in academic writing?

Yes, it is acceptable in academic contexts to highlight anomalies in data or behavior, as seen in publications from "MIT" and "Cornell University" cited by Ludwig.