weaken by + cause
Showing what causes weakness
By introduces the force, condition, or action causing weakening.
The economy was weakened by inflation.
Weaken by, weaken to, or weaken of
Weaken by and weaken to are both used in specific contexts. Weaken of is not standard in current English.
Quick answer
How to use weaken with prepositions
Use weaken by to show the cause or amount of weakening. Use weaken to for a final level or condition. Weaken of is nonstandard in modern English.
The bridge was weakened by the storm.
Sales weakened to their lowest level in years.
The disease weakened by age and stress.
Sales weakened to their lowest level in years.
The disease weakened by age and stress.
Choose the pattern by meaning
These forms are not interchangeable. Choose the construction by meaning, not by which preposition appears most often.
weaken to + level/state
Showing a new lower level
To introduces the result, degree, or condition after weakening.
The currency weakened to a record low.
weaken + object
Using weaken transitively without a preposition
Weaken often takes a direct object.
Lack of sleep can weaken the immune system.
be weakened by + process
Describing damage or reduction
Passive forms are common in formal and scientific writing.
The structure was weakened by corrosion.
See the difference in context
The same subject can take different constructions because each sentence answers a different question.
Construction
Example
Meaning
weaken by
The walls were weakened by fire.
shows the cause of weakening
weaken to
Demand weakened to a very low level.
shows the resulting level or condition
weaken of
This form is not standard in modern English.
generally considered incorrect
weaken from
He weakened from lack of food.
from can introduce a cause in some contexts
Common mistakes
Some combinations appear in real text but do not mean what learners often assume.
Using weaken of in standard English
Modern English does not normally use weaken of.
✕ The team weakened of injuries. ✓ The team was weakened by injuries.Confusing cause and result
By introduces the cause, while to introduces the final level.
✕ Sales weakened by a record low. ✓ Sales weakened to a record low.Omitting the object unnecessarily
Weaken often needs a direct object in active sentences.
✕ Poor nutrition weakens. ✓ Poor nutrition weakens the body.Using to with causes
To is not used for the reason something becomes weaker.
✕ The structure weakened to corrosion. ✓ The structure weakened from corrosion.Quick practice
Choose the expression that matches the intended meaning.
1. The building was weakened ___ the earthquake.
2. The currency weakened ___ its lowest point this year.
3. Which form is nonstandard in modern English?
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Frequently asked questions
Can weaken be used without a preposition?
Yes. It often takes a direct object, such as weaken the argument.
Is weaken to only for numbers?
No. It can also describe states or conditions, such as weaken to the point of collapse.
Can weaken from replace weaken by?
Sometimes. Weaken from is possible when describing a source or cause, especially with health or physical condition.
Related preposition guides
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