differences in the meanings between two sentences?

- He was reading a book, when somebody knocked on the door.
- While he was reading, somebody knocked on the door.

The other day I heard that a teacher on local radio program explained something on differences of the meaning between above two sentences. But somehow I failed to pay attention and listen to it as i was driving.
Please be kind enough to explain precisely.

[blacknomi]

Originally Posted by mrgoh

- He was reading a book, when somebody knocked on the door.
- While he was reading, somebody knocked on the door.

The other day I heard that a teacher on local radio program explained something on differences of the meaning between above two sentences. But somehow I failed to pay attention and listen to it as i was driving.
Please be kind enough to explain precisely.

'when' functions as a subordinate conjunction. If the adverbial clause introduced by 'when' is placed after main clause, you need not a comma. If the adverbial phrase is fronted, you should place a comma before the main clause.

He was reading a book when somebody knocked on the door.
When somebody knocked on the door, he was reading a book.


Somebody knocked on the door while he was reading.
While he was reading, somebody knocked on the door.


I don't see much difference between. Both mean during the time that someone was doing something, another event just happened.

[Francois]

- He was reading a book, when somebody knocked on the door.
- While he was reading, somebody knocked on the door.

The first one puts more emphasis on the interrupting action Eg.
"They were kissing each others when she remembered there was the last episode of Joe Millionnaire on tonight."
The 2nd one puts it on the action being interrupted. Eg.
"Her brother barged into her bedroom while she was shaving her moustache."

FRC

[MikeNewYork]

Originally Posted by Francois

The first one puts more emphasis on the interrupting action Eg.
"They were kissing each others when she remembered there was the last episode of Joe Millionnaire on tonight."
The 2nd one puts it on the action being interrupted. Eg.
"Her brother barged into her bedroom while she was shaving her moustache."

FRC

I'm afraid I don't see much difference between the sentences either. :?

[Tdol]

The second doesn't say what he was reading.

I think there pretty much the same.

[Francois]

Yes, they're certainly very close.
What about these two:

She was cooking the meal, when all of a sudden the pan caught fire.
=> I think there's an emphasis on the interrupting action.
All of a sudden the pan caught fire while she was cooking.
=> This is perfectly correct but doesn't sound as good, from a narrative point of view, does it? Even if you put the 'while' clause first, I don't think it's as good as the 1st sentence. Or maybe it's just me, oh well.

FRC