Doubles, Covering, and Blake’s Rule

Doubles are where Mexican Train stops being a simple matching game. They give you another go, they stop everybody else until they are dealt with, and they cause more table arguments than anything except the double blank. Here is how they work.

Playing a double stops the game

When you play a double — 8-8, say — it does not simply sit there. The double must be covered before normal play carries on, which means somebody playing a matching tile onto it. Under the usual rules the person who played it gets the first go at covering it, immediately, with a second tile from their own hand.

That is the part people describe as "a double gives you another turn". It is close enough, but the accurate version is that your turn does not end until the double is satisfied or you have run out of ways to satisfy it.

When you cannot cover your own double

You draw from the boneyard. If the tile you draw covers it, you play it and your turn ends normally. If it does not, your train opens up to everybody and your turn ends with the double still sitting there uncovered.

Now it becomes everyone else’s problem, and this is the bit that surprises new players: the next person must try to cover it too. They cannot ignore it and play somewhere else. If they cannot, they draw, their train opens up, and it passes on again. A stubborn double can go right round the table opening trains as it goes, which is either the best or the worst thing that happens all evening depending on whose train it is.

Branching

Once a double is covered, many groups let the train split into two branches from that point, each of which can then be played on independently. It gives everybody more open ends and keeps a crowded table moving.

Not everybody plays this way — some keep every train a single line, which makes for a tighter, slower game. Online it is a setting, Train Branching on Doubles, on by default and chosen when the game is created.

Going out on a double

Here is the rule that catches people. Under the common convention you cannot go out — play your last tile and end the round — while a double sits uncovered anywhere on the table, including one you just played.

So you may play a double as your final tile, but the round does not end. Your hand is empty and you carry on: drawing while the boneyard has tiles, and passing automatically once it does not, until the double is dealt with or the round blocks.

Blake’s rule

Which raises the obvious problem. What if you play a double as your last tile and the boneyard is already empty? Nobody can draw, so if nobody happens to hold a matching tile, that double can never be covered, and the round cannot end.

Blake’s rule is the usual fix: in exactly that situation — double as your last tile, empty boneyard — the round ends and you go out, as though you had covered it. It exists purely to stop the game deadlocking.

The online game applies it automatically and tells you: you will see "You’ve invoked Blake’s rule!" alongside the normal end-of-round results. If there are still tiles in the boneyard the ordinary rule applies instead, and you keep drawing.

Both parts are optional

The two doubles rules are separate settings online, and they can be set independently:

Setting	Default	With it off
Must satisfy doubles during the game	On	A played double does not lock the turn. Play just carries on.
Must satisfy doubles to go out	On	You can end the round on a double, and Blake’s rule never comes up.

Turning the first one off makes for a noticeably faster, gentler game, which some groups prefer with children or a big table. Both are chosen by whoever creates the game and apply to everyone in it.

For the game as a whole rather than just this rule, see how to play Mexican Train.

Keep reading

• How to play Mexican Train — the whole game
• How scoring works
• House rules and variations
• What the Mexican Train actually is