Sitting North, you are dealt a motley collection of cards:

♠️ K 2
♥️ K 9 7 5 2
♦️ 8 6 3
♣️ K 3 2

As South, partner opens 1♠️. Faute de mieux, you respond 1NT. Partner rebids 2♦️. More often than not, partner will hold five spades, four diamonds and anywhere from 12 to 18 high-card points.

What to do now? Instead of leaving partner high and dry in 2♦️, you rightly revert to 2♠️. Though you have more diamonds in your hand, this strategy is known as “false preference.”

There are two important reasons for your decision.

First, the 5-2 spade fit is probably easier to handle than the 4-3 diamond fit. Missing six trump, the most likely split is 4-2. At least you have an extra trump than their longer length when you are 5-2. Going back to opener’s first suit is a preference bid; partner should assume you have two spades.

Second, 2♠️ keeps the bidding open. Now partner will have the opportunity for a third bid with a second-bracket hand (16-18 HCP). Eighteen HCP will be the ceiling for such a sequence.

With 19, partner would have jump-shifted to 3♦️ (game-forcing) at the first opportunity. Opener will simply pass 2♠️ with a first-bracket hand (12-15 HCP).

Little do you know right now, but keeping the bidding alive will pay dividends unimaginable at this time. As things turn out, partner has the extra values for which you were hoping. Over your 2♠️, partner bids 3♥️! Obviously, 3♥️ implies a second-bracket hand. Otherwise your 2♠️ would have been passed.

You’ve learned even more than that. Partner has just “patterned out”; you’ve been sent a blueprint of the opener’s exact shape. You already know that partner holds five spades and four diamonds. How many hearts are being advertised? Exactly three! Partner cannot hold four hearts, or the rebid over your 1NT would have been 2♥️.

Opener’s hand is now clear: 16-18 HCP, five spades, four diamonds, three hearts and perforce one club. Again partner has patterned out. Now it’s incumbent on you to do something intelligent.

Partner’s third bid has demonstrated a 5-3 fit. With your nine HCP, there are at least 25 HCP in the partnership. You have an easy raise to 4♥️! Odd but true, you have more trump than declarer. As a result, declarer can’t score extra tricks by ruffing in dummy. All extra tricks must be ruffed in the closed hand. If declarer can manage to ruff a club in hand, 10 tricks should come home. In point of fact, they do!

When you hand appears as dummy, declarer sees 10 tricks available. There are six in hand: ♠️A, ♥️A, ♥️3 (for club ruff) and three diamonds. There are four in dummy: ♠️K and three trump.

The full deal:
Dlr: South
Vul: N-S

                          NORTH (You)
                         ♠️ K 2
                         ♥️ K 9 7 5 2
                        ♦️ 8 6 3
                        ♣️ K 3 2

WEST                                                 EAST
♠️ Q 10 8 6                                       ♠️ J 9
♥️ Q 4                                               ♥️ J 10 6
♦️ J 9 5 4                                          ♦️ 10 7
♣️ Q J 9                                            ♣️ A 10 8 6 5 4

                       ♠️ A 7 5 4 3
                       ♥️ A 8 3
                       ♦️ A K Q 2
                       ♣️ 7

The bidding proceeds as follows:

South               West             North            East
1♠️                  Pass             1NT                Pass
2♦️                  Pass             2♠️•              Pass
3♥️••               Pass             4♥️               All Pass

•  Classic preference
** A 5-4-3-1 pattern with five spades, four diamonds and three hearts. The bid implies a decent hand (16-18 HCP).

Result: +620 for North-South.

Nice score! Aren’t you glad you kept the bidding open with a mere preference? If you had not done so, the heart fit never would have come to light. With a mid-range hand, opener is entitled to a third bid over partner’s false preference. At that point, opener will strive to pattern out: transmit a mirror image of the shape of the hand so that the optimal contract can be reached. Today’s deal is a perfect case in point. Why flounder in a diamond partial when a more profitable heart game is possible?

What’s more, you have the bidding tools to find it!