Post date: Mar 28, 2013 8:7:58 PM
If partner says 4NT, he is usually using Blackwood Convention. Blackwood Convention asks for Aces.
If you have 0 or 4 aces, respond 4Club.
If you have 1 ace, respond 4Diamond.
If you have 2 aces, respond 4Heart.
If you have 3 aces, respond 4Spade.
He usually has interest in slam.
Circumstances where 4NT is NOT Blackwood Convention include:
After Jacobi Transfer
After 1NT