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Why this special treatment for mana-abilities? What are the design implications if they didn't go on the stack?

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3 Answers 3

up vote 15 down vote accepted

There are three reason I can think of:

  1. It would force arbitrary actions to be reversed.
  2. It would allow spells that haven't been fully cast to be countered.
  3. MTG already gives you enough of opportunities to react.

Forcing arbitrary actions to be reversed

Consider this rule:

601.2 [...] If, at any point during the casting of a spell, a player is unable to comply with any of the steps listed below, the casting of the spell is illegal; the game returns to the moment before that spell started to be cast.

Players can obtain mana in the middle of casting a spell[1]. If mana abilities used the stack, that means players would be able to cast spells in response. If the spell were to become unable to be cast, one would have to rewind all direct and indirect effects of those spells. Someone could have revealed private information, shuffled their library or lost the game as a result. How do you undo those?

Not only that, it would also make it far more likely for a spell to become unable to be cast, something that should never happen.

For example, consider this scenario where responding to mana abilities would be allowed.

  1. Alice only has a single creature on the 'field.
  2. Starts casting Altar's Reap.
  3. She activates a Swamp's ability.
  4. In response, Nancy casts Beacon of Destruction
  5. Nancy kills Alice's creature and shuffles his Beacon of Destruction into his library.
  6. Alice can no longer complete the casting of her spell (because she can't pay the additional cost), so the game rewinds to the start of the casting of the spell. Nancy needs to unshuffle his library to match the game state.

Allowing spells that haven't been fully cast to be countered

The first step of casting a spell[1] is to place it on the stack[2]. A spell is a card on the stack (or a copy of spell), so it could be the legitimate target of a Cancel cast in response to activating mana abilities. That's just too complicated and messy to allow.


Plenty of other opportunities to react

Activating mana abilities is not something someone one normally does for its own sake. It's done as part of something else, such as casting a spell. Allowing this to be interrupted would be detrimental to the game flow and would add confusion. There are plenty of other points at which players can respond.

The earlier problems only surface when activating mana abilities when one would not have priority under the current rules. Could the game allow players to respond to the activation of mana abilities performed when a player has priority? Yes, but it would often be hard to distinguish whether an activation occurred before or during casting. It's far simpler to have mana abilities never use the stack rather that having the player try to figure out whether one can respond to a particular activation or not.


Notes

  1. Or activating an ability. I'm only mentioning spells to keep it simple.
  2. The steps to casting a spell[1] are:
    1. 601.2a) Place card on stack.
    2. 601.2b-d) Make choices, including targets.
    3. 601.2e) Determine total cost.
    4. 601.2f) Activate mana abilities.
    5. 601.2g) Pay the previously determined cost.
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How do you interrupt paying a cost to make it unable to be paid? I was under the impression that this could not be done. –  Pow-Ian Sep 27 '13 at 18:00
    
@Pow-Ian, It's hard under current rules. I don't remember an example at the moment. Would probably have to involve continuous effects of cards sacrificed as an additional cost. –  ikegami Sep 27 '13 at 18:02
    
I think you are wrong about one statement: "The first step of casting a spell is to place it on the stack." according to 601.2 the first step is to put it on the stack and pay it's cost. that being true, you would never have a chance to use a mana ability while casting a spell if it had to be put on the stack because that would be taking another action before the first was complete. Also while paying a cost, no one can take any actions, so you can't make a cost unable to be paid while some one is paying it. –  Pow-Ian Sep 27 '13 at 18:05
2  
@Pow-Ian, When 601.2 says "To cast a spell is to take it from where it is (usually the hand), put it on the stack, and pay its costs", it's summarizing the entirety of casting a spell ("To cast a spell is") rather than describing the first the first step. The steps are explicitly stated to follow ("Casting a spell follows the steps listed below, in order"). Paying its cost is the 7th and last step of casting a spell. The steps are: 601.2a) Place card on stack. b-d) Choices are made including targets e) Determine total cost. f) Activate mana abilities g) Pay the previously determined cost. –  ikegami Sep 27 '13 at 18:30
    
Bob should probably be named "Norman", or "Neil", or "Nancy", to go with standard wizards rules scenarios labelling Active player with "A" names (Alice works fine) and Non-Active players with N names. Cryptography scenario naming is less relevant, and the naming allows you to convey extra clarification for free to more knowledgeable players. –  Patters Sep 30 '13 at 12:10

I think the simplest answer is that mana abilities are generally used while casting a spell to pay a cost. If they had to be put on the stack, then they could never be used while casting a spell because you would be taking another action before a previous action is complete.

601.2. To cast a spell is to take it from where it is (usually the hand), put it on the stack, and pay its costs, so that it will eventually resolve and have its effect. Casting a spell follows the steps listed below, in order. If, at any point during the casting of a spell, a player is unable to comply with any of the steps listed below, the casting of the spell is illegal; the game returns to the moment before that spell started to be cast (see rule 717, "Handling Illegal Actions"). Announcements and payments can't be altered after they've been made.

...

601.2h Once the steps described in 601.2a-g are completed, the spell becomes cast. Any abilities that trigger when a spell is cast or put onto the stack trigger at this time. If the spell's controller had priority before casting it, he or she gets priority.

If you follow 601.2 to it's conculsion you see that you could not activate the mana ability if it was not treated differently because you don't have priority while you are 'casting' a spell.

Yes you had priority when you started to cast the spell and you will have it again when you are done casting the spell, but while you are 'casting' it, (Paying its cost, choosing its targets etc) there is no passing of priority so no abilities or other spells can be used/cast.

So if it was treated like a normal ability, which you also can not activate while casting a spell, then you could never use them to pay a cost while casting a spell. they would always have to be used before you started paying the cost.

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It's silly to assume the game would allow you to activate mana abilities without allowing them to resolve (give you priority)! This is a perfectly correct yet perfectly useless answer. If you argument that we can't have X because we don't have necessary dependency Y, it just shifts the question to "Why can't we have Y?". But you left that unanswered. –  ikegami Sep 28 '13 at 2:41

There is some history behind the decision. Back in the dark ages of MtG rules, before sixth edition, there were a lot of rules that were unintuitive and confusing. With the release of Fifth Edition, a new type of ability was introduced,

Mana Sources: "Mana sources" are a new category of abilities. They include the ability of lands to be tapped for mana and all abilities that provide mana as interrupts. For example, Llanowar Elves's ability is now considered a mana source, but the ability of Ice Cauldron is not. Mana sources may be used whenever desired and may not be interrupted; there is no gap between playing the ability and resolving it. For example, you can't Rust a Mox; only continuous effects can stop a mana source from producing mana.

So, a Mana Source is anything that generated mana. Spells like Dark Ritual from earlier editions can be found with the card type Mana Source. Fifth Edition rules clarified that they may not be interrupted. This was necessary, because before the stack, Interrupts (depreciated, and later reclassified as Instants) were handled in batches

In the beginning, there was the batch. You played a spell, a flurry of "fast effects" were played in response, and then everything (well, everything except interrupts) resolved using the "last in, first out rule," with no chance of playing more spells in the middle. [...]

The timing issues presented by Red Elemental Blast and Blue Elemental Blast (and later, Hydroblast and Pyroblast) were particularly troublesome. Interrupts made sense when they targeted spells, but what happened when they began targeting permanents? Remember, removing the source of a fast effect does not remove the fast effect itself, but what about stopping the fast effect in response to it being played? [...]

Under the current rules, Mark taps his Prodigal Sorcerer in an attempt to deal 1 damage to Randy. In response, Randy plays Red Elemental Blast, targeting the Prodigal Sorcerer. This destroys the Sorcerer, but not before its "ping" effect goes onto the stack. That 1 damage is still dealt to Randy. Now, under the earliest Magic rules, Mark would announce the tapping of his Sorcerer, but Randy could say, "Hold on a minute! I want to interrupt your effect." This would stop the game, target the Sorcerer with Randy's Red Elemental Blast, and prevent the damage from ever being dealt. This created huge amounts of confusion over timing: The active player was supposed to have priority each turn, but interrupts being used this way seemed to contradict the rule. This problem, however, was corrected before interrupts were done away with entirely. The ruling said that if you targeted a permanent with an interrupt, the interrupt was played "as an instant."

So, under the pre-fifth edition rules, you could kill a Llanowar Elves or Interdict a land tapping for mana to prevent a player from generating enough mana to play a spell, and the game would have to backup to the point of the illegal action of casting a spell you couldn't pay the cost for. Sixth Edition rules and the stack did away with all this confusion. There are no longer batches and special timing rules for Interrupts/Instants, they all go on the Stack. Abilities that generate mana don't go on the stack, amd therefore cannot be responded to, removing the necessity to specify on the cards that they cannot target mana abilities.

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