Kathy Ide's Editing Tip #2

AS vs. WHEN

As (when used as a conjunction, as in “As this happened, that happened”) implies that the second thing occurred while (within the same time frame as, during the time in which) the first thing was in the process of happening.

When implies that the second thing happened at the same moment in time that the first thing happened (a specific time being the essential element).

Example:

"As the garage door came down (while it was in the process of coming down), the cat scurried under it."
vs.
"When the garage door came down (at the moment it touched the concrete), it hit the cat."