As a child, I had two walking speeds: lightning and snail. Snail was my standard; I would fall so far behind my mother in the grocery store that she could do her entire day’s shopping and find me back in the first aisle.
Lightning, the rarity, would occur only at specific places. Going to a Jets football game, I'd fly through the parking lot--a green blur. On occasion, I'd realize too late where we were going. Slow walking into a boring-looking building, then sprinting away as my mother chased me when I realized I was headed to a dentist's appointment.
You could always tell my attitude by how quickly I wanted to get to a place. In bridge, you should also try to convey to partner how you feel about your hand by altering how quickly you go (No, I'm not talking about your bidding tempo).
We teach beginners, “If you know what contract you belong in, bid it,” to prevent them from inviting with a game-forcing hand or responding 1NT with an opening notrump hand. As we get more sophisticated, we should get away from this thought process. Don’t assume that you know better than partner if partner is an unlimited hand (or virtually unlimited). If partner opens 1 and you have 13 HCP and three-card support, you know you belong in game and likely the game is 4, but you wouldn’t jump to 4--that would show a very different hand type.
Using game forcing tools like 2-over-1, Jacoby 2NT or fourth-suit forcing allows you to find a trump fit on a lower level. This means that you can explore for slam with hands that might be appropriate. What types of hands like to explore for slam? You should have something extra, beyond what partner might expect. “Extras” come in lots of shapes and sizes… specifically, you could have extra shape (singleton, a long side suit, etc.) or extra size (HCP), but you might also have extras in terms of how prime your hand is. Prime values are aces and kings. Consider these two hands after partner opens 1:
Which hand is more suitable for slam? The first hand. This hand has all aces and kings which is much better for slam bidding than the queens and jacks in hand B. Both of them are game forcing, but I wouldn’t consider hand B to have any extras. If the auction starts 1 P 2 P 2NT, hand A should next bid 3 and cooperate with a slam try, and hand B might now jump to 4.
Going slowly with good hands is an important way to find out if your side has the combined strength for slam. How do you slow down the auction once a fit has been discovered? Control bidding. Once you have set trump in an auction that cannot stop below game, then bidding a different suit shows a first or second round control in that suit. A control here is either an ace, a king, a singleton or a void. While control bidding only starts after 3 of your major, do not jump into a control. Jumping should show a splinter, even if it's not a double-jump as in 1-P-2-P-4.
You are not required to show your controls below game, so if you choose to get to the final contract more quickly, you are telling partner that you have the minimum of what you have shown. Bidding controls will, in addition to showing slam interest, allow you to know whether Blackwood is a good idea or not.
Larry has discussed the importance of control bidding for slam in this article, and knowing you have controls in each suit will allow you to have better Blackwood auctions. That's another good reason to treat a control-heavy hand as having extra. If you jump to game, partner is not going to feel comfortable exploring for slam if she has two small in a side-suit, or a hand that lacks keycards since the 5-level may not be safe.
Sometimes, both hands will be able to cooperate, but neither hand will have enough to insist on slam--that's fine, nothing is lost by cooperating for slam (although you give defenders a little bit of information). Don't feel that control bidding means that you expect to bid a slam, it simply tells partner that you have something about your hand better than expected given the auction to that point.