Usage of “when” or “while” in this context

Question

He left the house _ I was still sleeping

Would this sentence be better completed with when or with while?

Answer 1

The choice really hinges on the durative or punctual aspect of the particular verb (or verb construction, like was sleeping) in the adverbial clause. To illustrate the difference:

He left the house when the taxi arrived. (taxi arrived: punctual, point-in-time aspect)

He left the house while I was still sleeping. (I was still sleeping: durative, extended aspect)

There is sometimes a choice, to indicate the intended aspect:

He was in the playground when the children arrived. (They all came essentially at the same time.)

He was in the playground while the children arrived. (They came over a period of time.) (Here, children were arriving would probably be preferable.)