Dear FSW – Publisher:

You wrote:
> GREAT resource! Being an ex-Pat Brit in America gets me into all sorts of
> grammatical challenges. Your site confirmed my view that a comma follows
> the name in a greeting, and possibly a colon, but never, NEVER a period.
>
> But it offered no help on the which/what question. Is it “which house” or
> “what house”? “Which witch” or “what witch”? And why? TIA Frank
>

This is more a question of definition. Which used adjectivally means that there is a choice. “Which house?” would suggest that there was a group of houses and the asker was trying to make you be more specific. “Someone broke into a house on Drury Lane.” “Which house?” [which one?]

What does not necessarily mean there was a choice–in many cases the speaker might not have known there was a house. “What house?” would suggest that the speaker did not know there was a house there at all. “We saw the house sitting on the beach.” “What house?” [there’s a house on the beach?]