Mary, BIL member, asked the question:
Do you ask or show stoppers on the way to notrump?
Simple question, complex answer!
Best to consider a few auctions. Firstly, consider an auction where partner raises your minor suit and there is no opposition, say
Here bids would SHOW stoppers for notrump purposes. The same is true for the auction 1♣ (Pass) 2♣ (Pass) ?.
When there is no competition, you generally show stoppers unless the auction uses the fourth suit. For example,
2♦ is fourth suit forcing and asks opener to describe his hand further, in particular it asks whether opener has a diamond stop. Although fourth suit forcing does not deny a stop, it may express doubt over 3NT if the opener does not show a stop.
When there is competition there is a simple rule: if the opposition have shown ONE suit, then bidding that suit ASKS for a stop; if the opposition have shown TWO suits, then bidding that suit SHOWS a stop. For example,
Here, 3♠ asks for a spade stop.
Assuming that 2♦ shows the majors, then the opener bids the suit that he stops.