In the Friday Swiss at the Bermuda Regional, I had a chance to take partner's invitation at its full value and bid a nice slam, I just needed to think through the possibilities for what hand he could have to make that bid!
Because I have a balanced hand, regardless/especially because of that Spade suit, and I wanted to protect all those Kings, I opened 2NT (19-21). Partner bid Stayman (just regular) and I was happy to respond 3S. Now partner bid 4H.
OK, so what is that? This is a good thing to make sure you have clear with your partner, both technically and philosophically. I ate up a lot of bidding space, and necessarily so, when I opened 2NT. We still have some conventional treatments to help us find fits and explore for slam, but they're a little compressed, so it's important to realize what bids partner can use to tell us things about his hand. Let's think about the logical possibilities for what 4H might mean:
1. Natural. Nope, can't be that. It's true that partner might have both Majors, but if he did and I named one, then he could just raise. (There does exist Smolen over 2NT if you don't play Puppet Stayman -- a good reason not to play Puppet -- but it clearly doesn't apply here.)
2. Cuebid, agreeing in Spades. Well, there's a slim chance it could be this, but what would that mean partner actually holds? We're fortunate on this hand that our cards should help us to realize this isn't a cuebid. If it were, that would mean partner was interested in exploring for slam but didn't have either of the minor suit Aces. He just can't have a good enough hand for both of those conditions to be true when we have the KQ of Hearts also. But we're starting to think along the right lines, that partner might be slammish... (And on this line of thought, it's really important to note that neither 4C nor 4D over my 3S would be a cuebid in support of Spades either - rather, those are real suits, usually 6-cards, in hands that also held Hearts, hence the Stayman bid.)
3. Slam Invitation (artificial.) Ding ding ding! This is it. 4H is how partner agrees to Spades AND shows interest in exploring for slam. This is an important philosophical point that's been extrapolated from how we bid over 1NT as well - the idea being that when the Responder asks Stayman, gets a Major suit answer, and then bids the other Major, it's an artificial agreement in the Opener's Major and wants to look for slam, e.g., 1NT - 2C - 2S - 3H = Spade agreement, looking for slam (with several conventional followups possible, like Baze.) We just have a little less room over a 2NT opener, so we can't cuebid below game, but Responder can still try to get the slam ball rolling.
OK, so now that we have decided that partner is agreeing to our Spades and looking for slam, we can get really excited. For my passed-hand (therefore less than opening values) partner to be interested in slam, he must be looking at actual Keycards, and that's great for us because that's what we're missing. As long as we're the declarer, all our suits are safe from two quick losers when the lead comes into any of our Kings, which means we're safe at the 5-level, which means we can go ahead and ask partner about his number of Keycards. 4NT from us brings 5H (2 Keycards without the Spade Q) from partner, and that makes it easy for us to bid 6S. (We could entertain the idea of 6NT as well, but without knowing about any length in our side suits in partner's hand to generate tricks, we should probably stick to the 'safe' 6S.)
Partner's hand was:
Hooray! 6S is an easy make (particularly when the defense leads the HA.)
Now, some of you may wonder why partner asked Stayman in the first place. He reasoned that he didn't want to play in Spades unless we had a 5-4 fit (not really expecting that it was actually a 5-5 fit) and if we did have that fit, he would also be interested in a slam. The best way to find that out was to ask me about my Majors rather than show his 5-card Spades.