英语母语者讨论when doing, I do, I am doingI watch TV, when sitting in my sofa.

Flip a bitch:When driving, this is to indicate that you must make a U-turn.

问题

How to understand the usage of "when/while doing something" in grammar? For example,

I am watching TV, when sitting in my sofa.

I think "when" and "while" can never be used as prep.. They are conj. instead.

I remember seeing some explanation from a English grammar book, written for people speaking another language, which basicaly said "when/while doing something" is just a shorthand of "when/while somebody is doing something", where "somebody is" must appear in the main clause, otherwise this shorthand usage is not valid. For example, it is wrong to say

I watch TV, when sitting in my sofa.

because in the main clause there is no "be".

I would like to see if someone can concur or refute this explanation from rigorous English grammar point of view.

I remember seeing some explanation from a English grammar book, written for people speaking another language, which basicaly said "when/while doing something" is just a shorthand of "when/while somebody is doing something", where "somebody is" must appear in the main clause, otherwise this shorthand usage is not valid. For example, it is wrong to say

“I watch TV, when sitting in my sofa.”

because in the main clause there is no "be".

问答

This isn’t quite correct. It’s a bit better if the somebody appears in the main clause. The is doesn’t need to appear in the main clause at all.

Two examples:

An awesome sunset is a routine occurrence when chasing across the treeless Great Plains. (almost entirely ok)

This might sound a little bit odd to some people because the somebody (whoever

is chasing) is completely missing from the main clause. But to a lot of people it will

sound just fine. In ordinary speech, almost no one would notice.

One day, while looking through his grandparents’ attic, he found some old photographs.

(definitely ok)

This one is impeccable. The implied subject of looking is the he of he found. Note

that *“he was finding some old photographs” would be wrong.

Traditionally, while and when are called subordinating conjunctions. Some

modern grammarians call them prepositions. Whatever you call them, they are

followed by a clause: either an ordinary declarative clause (while Kaitlin worked on

her paper), an -ing clause (while watching TV), a past-participial clause (when forced

to respond), or a verbless clause (while in Rome, while an ice cream man in

Hawaii, when drunk). Except in the first case, the subject of

+1 Well said. Those things are called subject complements. To summarize, the essence of this kind of clause is that it is an elliptic clause, in which finite verb and subject are implicitly present but have been omitted for brevity. (On a side note, I and others with me object to calling anything a clause that doesn't have an explicit or implicit finite verb, as some people tend to do these days.)–Cerberus Mar 22 '11 at 0:10

@Cerberus Thanks. I think in grade school the term I learned was "predicate nominative"; apparently CGEL uses "predicative". Anyway I edited it out since CGEL agrees this is just an elliptic (they say "verbless") clause. (On the side note, you'll get no argument from me, but CGEL has a whole chapter on non-finite and verbless clauses.

I don't know what else to call them.)–Jason Orendorff Mar 22 '11 at 12:59

Your second sentence is equivalent to “I watch TV, when I am sitting in my

sofa”.

However, it has a different meaning from another possibility: “while sitting in

my sofa”.

The first one implies that, when you sit in the sofa, you watch TV, while the

second implies that watching TV is only one of your activities.