I'm no English teacher, but I was asked a question I couldn't answer. Can you think of a good explanation?

A sign on a plane:
"Keep seat belt fastened when seated"
A sign on a bus:
"Hold hand rails or strap while standing"

Why is one "ed" and one "ing"?


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ESL students laugh at the absurdity of "drive on the parkway" and "park in the driveway!"
And why isn't it "park on the driveway?" :P

The two main differences here are when and while. The former is an adverb and it cannot be followed by a present participle (the one with the ings). However, the latter is a conjunction, and like all conjunctions, they connect words together; therefore, using the present participle is allowed here. To add to my point, the word while is usually followed by the present participle and it would sound awkward if we used the past participle (the one with the eds).

For the other question, I assume it's park IN the driveway mainly because driveway is a subset of a bigger entity such as the private road.

Thanks for the insight, Ben.

What if both sentences contained while?

Keep seat belts fastened while seated.
Hold hand rails or strap while standing.

This might have been how I was originally asked, but I used when because it seemed a better fit as I typed.

"Keep seat belt fastened when seated."
'to seat (someone)" is the verb; 'seated' is the adjective, as in "A mannequin in a seated position."
The full sentence would be:
"Keep your seat belt fastened whenever you are in the seated position."

"Hold hand rails or strap while standing" = "…while in a standing position."
The adjectival form of 'to stand' is not 'stood', but 'standing' as in:
"The runners set off from a standing start."

Both are adjectives, and the difference is simply because the adjectival forms are different.

"Why isn't it "park on the driveway?"

Because 'on'' is used for permanent fixtures, and 'in' when something/someone is there temporarily.
We talk of 'the man in the street', 'rioters in the streets of London', but "The White House is on Pennsylvania Avenue."

A car is not a permanent fixture - that would defeat its whole purpose!
Hence, it is (temporarily) IN the driveway.