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Prepositions after verbs

harm by vs. harm to

Harm is commonly used as a verb without a preposition, while harm to is more common with the noun harm.

Quick answer

Do we say harm by or harm to?

As a verb, harm usually takes a direct object: harm someone. Harm to is common when harm is a noun. Harm by appears mainly in passive structures to introduce the cause or agent.

Smoking can harm your lungs.
The policy caused harm to small businesses.
Wildlife was harmed by the oil spill.
Too much heat can harm the device.

Choose the pattern by meaning

These forms are not interchangeable. Choose the construction by meaning, not by which preposition appears most often.

1
harm + person/thing

Using harm as a verb

Harm normally takes a direct object without a preposition.

The chemicals may harm marine life.
2
harm to + noun

Using harm as a noun

Harm to is common when talking about damage or negative effects.

The report examined the harm to public trust.
3
harmed by + cause

Showing the cause in passive voice

By introduces the thing or person causing the harm.

Several crops were harmed by frost.

See the difference in context

The same subject can take different constructions because each sentence answers a different question.

Construction
Example
Meaning
harm by
The forest was harmed by illegal dumping.
Used mainly in passive voice to show the cause or agent.
harm to
There was serious harm to the ecosystem.
Common with the noun harm, not usually with the verb.
harm someone
The scam harmed many customers.
Standard verb pattern without a preposition.
do harm to
These chemicals do harm to aquatic life.
Fixed expression using the noun harm.

Common mistakes

Some combinations appear in real text but do not mean what learners often assume.

Adding to after the verb harm

The verb harm usually takes a direct object.

✕ This could harm to children. ✓ This could harm children.

Using harm by in active voice unnaturally

By is usually used in passive structures.

✕ They harmed by pollution the river. ✓ They harmed the river through pollution.

Confusing verb and noun structures

Harm to belongs with the noun harm.

✕ The fire harmed to the building was severe. ✓ The harm to the building was severe.

Leaving out the object after harm

Harm usually needs a person or thing affected.

✕ Smoking harms. ✓ Smoking harms your health.

Quick practice

Choose the expression that matches the intended meaning.

1. The explosion caused serious harm ___ nearby homes.
2. Strong sunlight can harm ___ skin.
3. The crops were harmed ___ insects.

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Frequently asked questions

Is harm to correct?

Yes, especially when harm is used as a noun, as in harm to the environment.

Can harm be used without a preposition?

Yes. As a verb, harm usually takes a direct object.

When do we use harmed by?

Use harmed by in passive sentences to show the cause or source of damage.

hack-into-by-at-to, in "haggle with" or "haggle for"? "hail from" or "hail as"? hamper by, due, in, for or throughout? "handle by" or "handle in"? hang in, from, over, around or onto? "happen to" or "happen in"? harass by, in, at, for or with? harvest from, in, for, at or by? hasten to, by, from, after or into? hate on, for, by, about or in? haul in, before, by, into or over?

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