Duplication

You can try to play backgammon without ever taking a risk, but you will not get far that way. Winning requires risk. What matters is whether you take risks blindly or in a way that keeps them as small as possible, and duplication is one of the main tools for the second approach. With practice you will not need to think about it as a separate technique: it simply becomes part of how you choose your moves.

What is duplication?

Duplication is one of the harder ideas for beginners to grasp, because it is not a plan like a priming game or the blitz. It is a principle you apply inside any plan.

In short, duplication means arranging your checkers so that the numbers your opponent wants for one purpose are the same numbers he wants for another purpose. He can use a given number only once, so he has to choose. For example, if a four lets him hit your blot, and a four is also the number he needs to make an important point, the two good uses of the four overlap. Instead of two separate sets of good rolls, he has one, and many of his rolls force a compromise.

The opposite principle, spreading your own checkers so that as many of your numbers as possible are useful, is called diversification.

Voluntary shots

Sometimes you could play completely safe, but a bolder move gives you a better position, at the cost of a blot. Duplication helps you decide where that blot should go.

Imagine you have just entered a checker from the bar and have one number left to play. A safe move exists that leaves no shot but does little for your position. Another move brings a builder into your outfield, where it will help you make a key point next turn, but leaves it four pips from one of your opponent's checkers. A direct four hits 15 of 36 rolls, about 42 percent, which sounds like a lot.

Now look at what your opponent needs fours for. Suppose his most important goal this turn is to make his own 5-point, and the only way to do that is also with a four. He cannot do both with one four. If making his 5-point is worth more to him than hitting your builder, his correct play with most fours is to make the point and leave your blot alone. Your real risk is much smaller than 42 percent, and if he does not hit, your builder helps you make a strong point next turn.

That is duplication at work: by putting your blot where the same number is needed elsewhere, you make his good rolls overlap.

Forced shots

Often you have no choice and must leave a blot somewhere. Duplication tells you where.

Suppose you have a straggler that needs to escape past one of your opponent's points, but you rolled a small number and cannot get it to safety. The natural instinct is to move it as close to the safety point as possible. Instead, look at your opponent's priorities first.

Perhaps he has a blot in his own home board that he badly needs to cover before he can afford to hit, because if he hits loose and you then return the hit from the bar, his position collapses. Covering that blot needs certain numbers, say fives. If you leave your straggler where he also needs fives to hit it, then most of his fives must choose between covering and hitting, and only a few rolls let him do both. If you leave the straggler somewhere else, a three away for example, then threes hit and fives cover, and rolls like 5-3 do both jobs at once.

Leaving the blot in the "duplicated" spot can therefore be safer in practice, even when it looks riskier at first glance.

How to start using it

Conclusion

It takes some games before you start seeing chances for duplication, and some more before you choose correctly in the moment. Do not worry about that. Keep the idea in mind, look for it when you leave a shot, and it will become natural. Reviewing your games with an analysis program is a good way to spot positions where duplication changed the best move; see our software review for options.