Green Glass Doors

A Membership Game

Green Glass Doors is an example of a secret rule game.

What is a secret rule game?

A secret rule game is a playful, often puzzling group activity where one or a few players know a secret rule that determines what fits or happens in the game, while the rest of the players must figure it out through observation and deduction. The fun lies in the mix of confusion, clever hints, and the "aha!" moment when players crack the code, making these games perfect for sparking laughter and creative thinking in social settings.

Like all secret rule games, Green Glass Doors is played in a group where some, but not all, players know the secret rule. Green Glass Doors is also an example of a Membership game, because of the form that the core gameplay takes.

What is a Membership game?

In a Membership game, gameplay revolves around organizing things into groups based on a specific quality. For example, whether something can go through the Green Glass Doors. The quality varies from game to game, but typically, anything that can be discussed, be it a person, place, thing, or otherwise, may or may not possess that quality. In this way, that thing can be considered to be a member of the class of things possessing that quality, or not. Players who know the secret rule understand the criteria that determines membership, and can easily determine whether anything put forward by the other players should be a member of the class or not.

How to play Green Glass Doors

Gameplay revolves around players gathering examples of something that either can go through the Green Glass Doors, or not. There are two ways these examples can be provided.

The first option is that a player who already knows the secret rule can volunteer an example. All players should know which other players claim to know the secret rule, and will know to trust the examples accordingly. Players who claim to know the rule, but don't actually, will quickly be discovered by players who actually know the rule, and their examples will be called out as incorrect. When providing examples, it may be helpful for players to provide examples of two things that are similar in some respects, but only one of which can go through the Green Glass Doors.

The second option is for players who do not yet know the secret rule to suggest something new and ask the players who do know the secret rule whether it can go through the Green Glass Doors. Typically, this question will be answered the same way and at the same time by all players who know the secret rule, which is helpful to convince new players that the rule is not arbitrary, and that it is an easy process to determine whether something can go through the Green Glass Doors. While questions will almost always be answered with "yes" or "no", there are some cases where the answer may be less concrete, which can give players clues about the secret rule.

The game ends when all players know the secret rule, and can agree on what can go through the Green Glass Doors reliably. These players will no longer be able to play Green Glass Doors, but don't worry, there are plenty of other games!

What is the secret rule?

Click the link below to show the secret to Green Glass Doors. Remember, these games are played by learning the rule, and if you don't already know it, revealing it here will rob you of the opportunity to learn the rule by playing. If you already know the rule, click the link to see some tips and recommendations that can't be provided without spoiling the secret.

Reveal the secret rule to Green Glass Doors

The secret to Green Glass Doors

What determines whether something can go through the Green Glass Doors has to do with the content of the thing being suggested or asked about.

If something is spelled with double letters, it can go through the Green Glass Doors.

Considerations

One thing to consider when playing Green Glass Doors is whether all the words in a phrase or description have to have double letters for that thing to pass through, or whether any word in the phrase having double letters is good enough. For example:

Can Cookie Monster go through the Green Glass Doors, even though a Monster can’t?

My recommendation is to require all words in a phrase to have double letters to go through the doors, since the title of the game has so elegantly managed to include double letters in all 3. If you want to play a version of the game where double letters in one of the words is good enough, check out the other games that share the rule.