Guard against is the standard pattern when talking about protection from danger or harm. Guard by is not a normal active verb-preposition combination.
Use guard against to mean protect from danger, risk, or harm. Do not normally use guard by after the active verb guard. However, by can appear separately in passive expressions such as “The gate is guarded by security staff.”
These forms are not interchangeable. Choose the construction by meaning, not by which preposition appears most often.
Against introduces the threat or risk.
Guard can take a direct object without a preposition.
By introduces the agent in passive structures.
The same subject can take different constructions because each sentence answers a different question.
Some combinations appear in real text but do not mean what learners often assume.
Use against for threats, or use a passive structure with by.
✕ They guard by theft. ✓ They guard against theft.Guard often needs the thing being protected.
✕ The soldiers guarded against all night. ✓ The soldiers guarded the bridge all night.By belongs naturally in passive constructions.
✕ Security guards by trained staff. ✓ The area is guarded by trained staff.Choose the expression that matches the intended meaning.
Paste the complete sentence below. Linguix checks the preposition together with grammar, spelling, punctuation, and style.
Usually, yes. It refers to protection from risks, threats, or unwanted outcomes.
Not as a normal active verb-preposition pattern. Use “guard against” or a passive form like “guarded by.”
Not always. You can say “guard the door” with a direct object.
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