Bridge & other card games/bidding 4 no trump asking for aces
is there any time this cant be used. thank you
Consider cases where partner opens 1NT or 2NT, or after he opens one of a suit and shows a specific point range by rebidding 1NT or 2NT. In these specific situations, a jump to 4NT would not be Blackwood -- it's a natural raise of notrump that invites partner to bid 6NT if he's at the top of his point range. Partner can pass 4NT if he has a minimum notrump opener or rebid. In these situations use the Gerber convention to ask for aces.
In general, 4NT asks for aces if a trump suit has been agreed upon. Alternatively, if the opener has opened or rebid notrump showing a specific point range then 4NT is a quantitative bid and 4C Gerber asks for aces.