Editing Blue dog rule

[[Image:TraderOld2.jpg|thumb|right|200px|[[Trader]] (early version), the card that most often invokes this rule.]]

The "'''blue dog rule'''" is a ruling by [[Donald X]] on what to do when an ability has an effect either based on a card it's gaining, but the card to-be-gained is never actually gained for one reason or another.  In this case, the ability has no effect, since it did not gain a card.

The archetypal example of this rule is the interaction between {{Card|Ironworks}} and the {{Card|Trader|oi=2|early version of Trader}}. If you would gain a card with Ironworks, and then reveal Trader to gain a {{Card|Silver}} instead, you never actually gained anything with Ironworks, so Ironworks fails to give a bonus effect based on the type of the card gained. Since the 2020 revision of Trader, however, the rule no longer applies to it, since the revised version of {{Card|Trader}} does not prevent you from gaining a card. 

It is called the "blue dog" rule because when [[Hinterlands]] was first released, Donald X posted a bizarre analogy about walking a [[blue dog]] to try to explain the interaction.

== List of cards that can invoke the Blue dog rule ==
=== Gaining-hinderers ===
* {{Card|Possession}}
* {{Card|Trader|oi=2|Trader (early version)}}
If a chosen Supply pile is empty, or a [[split pile]] with no more copies of the desired card remaining, this also hinders gaining. Trying to gain from an empty pile requires some shenanigans, such as triggering a {{Card|Sheepdog}}, played {{Way|Way of the Mouse}} as {{Card|Lurker}}, to trash the last copy of the card you were trying to gain.
=== Gain-effect cards ===
This applies to any cards with an "If you do" or similar clause preceding an effect dependent on a card gain (such as {{Event|Ritual}}), and it's usually quite clear that nothing happens, because of this phrasing.  However, a few cards have no such phrasing, leading to potential ambiguity; this ruling was given specifically for these kinds of cards:
* {{Card|Ironworks}}
* {{Card|Replace}}
* {{Card|Horn of Plenty}}
* {{Card|Messenger}}
* {{Event|Seaway}}
* {{Card|Groom}}
* {{Event|Reap}}
* {{Event|Summon}}

== Trivia ==
Donald X.'s original quote:
{{Quote
|Text=If I say, "feed the blue dog, then take it for a walk," "it" refers to the blue dog, including its blueness, but "it" does not mean "the dog you fed." We are talking about a blue dog, and I am giving you two commands concerning it. Feed it, walk it.
|Name=Donald X.
|Source=[http://boardgamegeek.com/article/7743728#7743728 Ironworks and Trader]
}}
While the quote provided the name for the ruling, afterward Donald X. changed his position on how the interaction should work to how it stands today.

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