State-Based Actions

Interactions · intermediate

State-based actions (SBAs) are automatic game-state checks that run constantly. They don't go on the stack -- they just happen as soon as conditions are met, whenever a player would get priority.

What they check

The most common SBAs:

• A player with 0 or less life loses the game.
• A player who has tried to draw a card from an empty library loses.
• A player who has 10 or more poison counters loses.
• A creature with toughness 0 or less is put into its owner's graveyard.
• A creature with lethal damage marked on it is destroyed (unless it has indestructible).
• A planeswalker with 0 loyalty is put into its owner's graveyard.
• The "legend rule" -- if a player controls two legendary permanents with the same name, they choose one to keep; the other goes to the graveyard.
• Aura-on-illegal-target -- an aura attached to something illegal is put into its owner's graveyard.
• Tokens that have left the battlefield cease to exist.

When they run

State-based actions are checked before any player gets priority. So when a spell resolves, the game first checks all SBAs (and triggers any abilities that trigger from those state changes), then gives priority back.

Why this matters

Almost every "weird interaction" question in Magic comes down to SBAs:

• "Why didn't my creature die when blocked?" -> SBAs hadn't been checked yet, or damage wasn't lethal.
• "Why did my Solemnity stop that?" -> A trigger references counters, which SBAs handle.
• "Why did both legends die?" -> The legend rule fires when one player has two of the same name. If two different players each control one, they're fine.

Triggered abilities vs SBAs

• Triggered abilities ("when this dies, draw a card") use the stack and can be responded to.
• State-based actions don't use the stack. You can't respond to a creature dying from lethal damage; it just dies.

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