warn of + danger
Mentioning a possible risk or threat
Warn of is followed by a danger, consequence, or negative event.
Scientists warn of rising sea levels.
Warn of vs warn against
Warn of introduces a danger or possible problem. Warn against advises someone not to do something because it may be dangerous or unwise.
Quick answer
When to use warn of and warn against
Use warn of to mention a danger, risk, or negative possibility. Use warn against to advise someone not to take an action or follow a course of action.
Experts warned of severe flooding.
Doctors warn against smoking during pregnancy.
The guide warned of delays on the route.
Doctors warn against smoking during pregnancy.
The guide warned of delays on the route.
Choose the pattern by meaning
These forms are not interchangeable. Choose the construction by meaning, not by which preposition appears most often.
warn against + action
Advising someone not to do something
Warn against is followed by an activity, behaviour, or plan.
Police warned against leaving valuables in cars.
warn someone about + topic
Warning a person about something specific
Warn someone about is common when the listener is named directly.
She warned me about the scam.
warn someone not to + verb
Giving direct advice or instruction
This structure gives a clear negative instruction.
The teacher warned students not to cheat on the exam.
See the difference in context
The same subject can take different constructions because each sentence answers a different question.
Construction
Example
Meaning
warn of
They warned of a possible shortage.
describes a danger or negative possibility
warn against
They warned against buying fake tickets.
advises people not to do something
warn about
She warned us about the icy roads.
general warning about a topic or situation
warn someone of
He warned them of the consequences.
formal structure meaning inform someone about a danger
Common mistakes
Some combinations appear in real text but do not mean what learners often assume.
Using warn against with a danger noun
Warn against usually introduces an action, not a danger itself.
✕ Experts warned against storms. ✓ Experts warned of storms.Omitting the object after warn against
Warn against normally needs an action or behaviour.
✕ They warned against. ✓ They warned against travelling at night.Confusing warn of with direct advice
Use warn against when advising people not to act.
✕ Doctors warned of eating too much sugar. ✓ Doctors warned against eating too much sugar.Using incorrect infinitive structure
Use warn someone not to do something for direct instructions.
✕ She warned me to not drive fast. ✓ She warned me not to drive fast.Quick practice
Choose the expression that matches the intended meaning.
1. Meteorologists warned ___ heavy snow this weekend.
2. The coach warned players ___ arguing with the referee.
3. She warned me ___ the hidden fees.
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Frequently asked questions
Can I say warn about instead of warn of?
Yes. Warn about is common in everyday English and often overlaps with warn of.
Is warn against followed by a noun or verb?
It is often followed by a noun phrase or an -ing form, such as warn against fraud or warn against driving fast.
Is warn of formal?
Warn of is slightly more formal and common in news or official statements.
Related preposition guides
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