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Prepositions after verbs

How to use “detect by” and “detect in”

Detect by and detect in are both possible, but they express different ideas. By usually refers to a method, while in refers to the place or source where something is found.

Quick answer

Use “detect by” for method and “detect in” for location

Detect by explains how something is discovered. Detect in refers to the place, substance, or group where something is found.

The illness was detected by a blood test.
Scientists detected traces of gas in the atmosphere.
The error was detected by the software.

Choose the pattern by meaning

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

1
detect by + method

Explaining how something is discovered

By introduces the tool, process, or method used for detection.

The leak was detected by thermal imaging.
Fraud was detected by an automated system.
2
detect in + place or substance

Showing where something is found

In introduces the environment, sample, or group where something is detected.

Researchers detected bacteria in the water supply.
The defect was detected in several units.
3
detect + object

Using detect with a direct object

Detect often takes a direct object without another preposition.

Doctors detected the infection early.
The sensor detected movement near the entrance.

See the difference in context

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

Construction
Example
Meaning
detect by
The problem was detected by routine testing.
By introduces the method or agent used for detection.
detect in
Lead was detected in the paint.
In introduces the place or material where something is found.
detect with
The disease was detected with advanced equipment.
With can introduce an instrument, although by is often preferred for methods.
detect through
The pattern was detected through careful analysis.
Through emphasises the process leading to discovery.

Common mistakes

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

Using “by” instead of “in” for location

Use in when naming the place or substance where something is found.

✕ Smoke was detected by the kitchen. ✓ Smoke was detected in the kitchen.

Using “in” for a detection method

Use by to describe the method of detection.

✕ The fault was detected in a scanner. ✓ The fault was detected by a scanner.

Adding unnecessary prepositions

Detect can directly take an object.

✕ The system detected about an error. ✓ The system detected an error.

Confusing “by” and “with”

Both are possible, but by is more natural for methods and processes.

✕ The fraud was detected with regular monitoring. ✓ The fraud was detected by regular monitoring.

Quick practice

Choose the expression that matches the intended meaning.

1. The virus was detected ___ a laboratory test.
2. High sugar levels were detected ___ the samples.
3. The software detected the error ___ seconds.

Check your sentence in context

Paste the complete sentence below. Linguix checks the preposition together with grammar, spelling, punctuation, and style.

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Frequently asked questions

Can both “detect by” and “detect in” be correct?

Yes. They are used for different meanings: method versus location or source.

Is “detect with” wrong?

No. It is acceptable when referring to an instrument, although by is often more natural for methods.

Do I always need a preposition after “detect”?

No. Detect often takes a direct object, such as “detect a problem.”

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