We warned her against the danger vs We warned her on the danger

The correct phrase is 'we warned her against the danger.' 'Against' is the preposition used after 'warn' to indicate the thing or action that is being cautioned about.

Explained by Michele A.
Editor at TextRanch

Last updated: March 24, 2025 • 5432 views

This phrase is correct and commonly used in English.

"We warned her against the danger"

This phrase is used to indicate that someone was advised or cautioned about a specific danger or risk.

Examples:

We warned him against investing in that company.
The doctor warned her against eating too much sugar.
They warned us against traveling alone at night.
She warned her friend against trusting strangers.
The teacher warned the students against cheating on the exam.

Show examples from the web [+]

Ms Muscardini "warned against the dangers of theocracy but also excessive secularism".
Two judges warned against the dangers of "goldplating", ie. adding further requirements in the national transposition measures which were not contained in the original Directive.
This has been pointed out by a number of NGOs which, without directly opposing the change, have warned against the danger of this trend leading to a lower level of protection in a number of Member States for asylum seekers and refugees.
He also warned against the dangers of protectionism and, indeed, saw a renewed Lisbon Strategy as the only way forward for the EU, with the emphasis on higher standards of education and training, more research and innovation and completion of the internal market.
Citizens in Europe are not being properly warned against the potential dangers of mobile phone technology.
The men attacked her and warned her against going out at night and taking up a 'party' lifestyle.
We warned the British Labour Government months ago about the dangers of an open-ended commitment of British troops to Sierra Leone.
We warned against the consequences of liberalising international trade in agri-foodstuffs.
Just yesterday she was again threatened by the military authorities, who warned her that if she continues to speak out against the government she will be imprisoned.
In the period leading up to the Summit, we warned against the EU turning itself into a fully-fledged defence alliance on a number of occasions.
After that, it's you and her against the system.
Propping her against the pillow, spread her legs apart.
She always acted like it was her against the world.
Cundalini, put her against the post.
He pushed her against the wall so hard.
Particularly sensitive risk groups must be protected against the dangers which specifically affect them.
Subject: Protecting consumers against the dangers of sunbeds
We will balance the danger of killing Lieberman... against the scientific validity of your project.
At the time of the Seville European Council, we warned of the danger of making cooperation for development conditional upon the control of immigration on the part of the countries in which it is generated.
Concepcion, the owner, defends her against the tyrant.

This phrase is not correct in English. 'On' is not the appropriate preposition to use after 'warn' in this context.

"We warned her on the danger"

Show examples from the web [+]

At the time of the Seville European Council, we warned of the danger of making cooperation for development conditional upon the control of immigration on the part of the countries in which it is generated.
It means we've been warned of the dangers.
You were warned of the danger, and you refused to believe.
I warned about the dangers of sleep deprivation.
Your father claims that I have warned you of the dangers of marriage.
Certainly, everyone ought to be warned about the dangers of the sun and that is why I am very much in favour of national campaigns.
Liberal Democrats have long warned of the dangers which caught the Council unaware and the Commission wrong-footed.
The doctor warned him of the dangers of smoking.
Lucas Henry would have been aware of the danger you warned me about.
My father has warned people about the dangers... of experimenting with DNA viruses for years.
I warned you of the dangers of the pits.
Busmalis warned him of the dangers, but they were so anxious to go.
I've warned you of the dangers disrespectable magic can pose.
For the Liberals, Herman VERMEER (NL) warned of the dangers of exporting the problem of poorly conditioned vessels outside the EU.
She warned of the danger of replacing the "iron curtain" with a "silver curtain".
Ms Muscardini "warned against the dangers of theocracy but also excessive secularism".
Two judges warned against the dangers of "goldplating", ie. adding further requirements in the national transposition measures which were not contained in the original Directive.
Yes, everyone should be warned about the dangers of the sun, but that should not be up to employers.
The Portuguese Director-General for Health has warned consumers of the dangers of the so-called 'Mineral miracle solution'.
We warned the British Labour Government months ago about the dangers of an open-ended commitment of British troops to Sierra Leone.

Alternatives:

we warned her about the danger
we warned her of the danger
we warned her regarding the danger
we warned her of the risks
we warned her about the potential harm

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We warned her against the danger vs We warned her on the danger

"We warned her against the danger"

"We warned her on the danger"

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