In Modern Acol, the prevalent bidding system in the UK, you open the higher-ranking of two equal-length suits, thereby placing the emphasis on the major suits.

I am often asked why not open 1 ♣ with, say, 15 points and four-four in ♣ + ♠ on grounds of economy. The reason lies in your basic strategy. Being balanced, you should rebid notrumps. But if you rebid 1 NT over a 1 ♦/♥ response (partner would respond 1 ♦/♥ with four-four in ♦/♥ + ♠), you may miss a spade fit, a big disaster. Far better simply to open 1 ♠: the spade fit will now quickly be found (or not).

With four cards both majors (eg 15 points 4 ♠4♥ 32), however, it is best to open 1 ♥, giving partner a cheap chance to introduce spades. If he responds, say 2 ♣, you will not now need to bid your spades, instead going ahead and rebidding 2 NT to show your balanced hand.

Open 1 ♠ and you may miss a heart fit (a 2 ♥ response requires more than minimal responding values and also a five-card suit).

Exercise: What would you open with these hands?

With Hand (i) open 1 ♥, planning to rebid notrumps.

With Hand (ii) open 1 NT (trap!); one more point and you’d open 1 ♠.

With Hand (iii) open 1 ♥, the four ♥ - four ♠ exception.

With Hand (iv), however, five-five in ♥ + ♠, it’s back to the higher-ranking rule: 1 ♠. Opening 1 ♠ then bidding 2 ♥ is more economical than 1 ♥ then 2 ♠, allowing partner to give a preference back to the first suit at the two-level.