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In the city of Potsdam I have seen the following label on the main station building: "This area is being supervised by video".

The meaning of the phrase is pretty clear, but can "video" be really used as an actor for the action of supervising?

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Is Potsdam really a city? :D – Glen Wheeler May 23 '11 at 9:50
It is even considered to be a capital :) en.wikipedia.org/wiki/Potsdam – Andrey Adamovich May 23 '11 at 12:41
up vote 8 down vote accepted

The phrase "This area is being supervised by video" doesn't refer to the video doing the supervision, but rather to the method of supervision. I.e. "I am improving by learning" doesn't refer to the "learning" doing the improving, but you improving through the method of learning.

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The trouble with the sentence is not in the 'by' phrase, it's in the verb.

In English, inanimate objects are not supervised, only people or animals or inherently active things like industrial processes. "Supervise" suggests the thing being supervised has a life of its own--and also usually that the thing's activities are being shaped by the supervisor. An 'area' is not one of those things.

The correct phrase would be

This area is being monitored by video.


This area is being surveilled by video.

Now consider

Activities in this area are being supervised by video.*

Slightly better grammatically, but it sounds like whoever put up the sign is taking responsibility for the activities, rather than just watching what happens. So that one won't work.

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Surveil/surveille does exist as a backformation from surveillance, but I've never seen a context where watch wouldn't be better. – TimLymington Oct 15 '12 at 20:46
+1 Good point, there. – Kris Oct 16 '12 at 4:47

Adding to the previous answers - by, and prepositions in general, are function words (except, arguably, in their central locative and directional - and perhaps in their temporal - senses) rather than content words. (See the fine Wikipedia article at http://en.wikipedia.org/wiki/Function_word .) Their usages are so diverse that a section of a grammar rather than a brief entry in a dictionary is required to even come close to a comprehensive treatment (see, for instance, http://classiclit.about.com/library/bl-etexts/wmbaskervill/bl-wmbaskervill-grammar-parts-prepositions.htm ). (Though the AHDEL and Collins do a commendable job.)

A few more examples where the preposition by is obviously not being used in the agentive sense (eg She was bitten by the dog.):

We can get in touch by radio. (instrumental)

There is a deer by the river. (locative)

We went by Leicester. (locative/directional)

It hunts by night. (temporal - habitual)

You must be there by 9 pm. (temporal - limiting)

They all reported, one by one. (sequencing)

It missed by a whisker. (degree)

'All words are infinitely polysemous' - and prepositions more than most.

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+1 By the way (I-don't-know-which), there are usages that are taken to be more idiomatic than strictly grammatical. – Kris Oct 16 '12 at 4:50

Yes Andrey, in the same way a picture can be taken by a camera.

In this statement, by answers the question 'How'.

How is this area being supervised? - By video

How are you going to get there? - By car

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