X cannot detect when Y is present

[manhhiep2509]

Hello.

The below sentence is choice B of question 80 in verbal review 2.

"X cannot detect when Y is present"

I eliminated the choice because I think that "detect" need an object. In the choice, "when y is present" is adverb modifying "detect", so we do not know what X cannot detect.

Is my interpretation correct?

Thank you.

[RonPurewal]

Hello.

The below sentence is choice B of question 80 in verbal review 2.

"X cannot detect when Y is present"

I eliminated the choice because I think that "detect" need an object. In the choice, "when y is present" is adverb modifying "detect", so we do not know what X cannot detect.

Is my interpretation correct?

Thank you.

Well, you need to be careful about generalizing here, because these kinds of things can act as nouns.

E.g.,

Prosecutors need to determine the facts.
("the facts" = noun)

Prosecutors need to determine when Joe arrived at the house and whether he had the gun.
("when xxxx" and "whether yyyy" act as nouns)

Many of these things can also act as adverbs, as you've pointed out (e.g., I called the police when Joe arrived at the house).

I don't have that book in front of me at the moment, but, even from the tiny snippet you've given here, it's pretty obvious that X is something that's supposed to detect Y itself (or the presence of Y), not the timeframe when Y is there.
If the sentence were intended to refer to the timeframe, then this construction could be correct, as in the first example above.

[manhhiep2509]

I don't have that book in front of me at the moment, but, even from the tiny snippet you've given here, it's pretty obvious that X is something that's supposed to detect Y itself (or the presence of Y), not the timeframe when Y is there.

I do not understand why you said that "X detect the presence of Y, not the timeframe when Y is there".

"when" indicates timeframe, so I conceive the sentence "X cannot detect when Y is present" as "X cannot detect the moment when Y is present".

Please explain further.

[RonPurewal]

Well, we'd need a specific context (since "X" and "Y" have no inherent meaning), but it's unlikely that "detecting a timeframe" makes any sense.

For instance, let's say you have a Geiger counter. The Geiger counter doesn't "detect the moment when radiaton is emitted"; it detects the radiation that is emitted.

Or a smoke alarm. It doesn't "detect when there's a fire"; it detects fires.

Etc.

[RonPurewal]

The only situation in which "detect when..." would make sense would be a situation in which someone is trying to reconstruct the actual timeframe of an event.... and perhaps not even then.

E.g., a police detective can examine the body of a murder victim to determine when the victim died -- i.e., to determine the exact (earlier) time of death.
Even in this circumstance, "detect" still doesn't really make sense, because the detective is not directly detecting (= sensing, perceiving) the time of death; (s)he is indirectly ascertaining it from evidence.