Since the last Rule of Law dealt with the difference between playing something and putting it into play, it only makes sense to have this one deal with the actual mechanics of playing spells and abilities. Most spells and abilities don’t need the detail I am about to describe, but those that do have important subtleties that make them special.
The relevant section from the Magic Comprehensive Rulebook (there’s a lot here, but it’s all important):
409. Playing Spells and Activated Abilities
409.1. Playing a spell or activated ability follows the steps listed below, in order. If, at any point during the playing of a spell or ability, a player is unable to comply with any of the steps listed below, the spell was played illegally; the game returns to the moment before that spell or ability was played (see rule 422,”Handling Illegal Actions”). Announcements and payments can’t be altered after they’ve been made.
409.1a The player announces that he or she is playing the spell or activated ability. It moves from the zone it’s in to the stack and remains there until it’s countered or resolves. In the case of spells, the physical card goes onto the stack. In the case of activated abilities, the ability goes onto the stack without any card associated with it. Each spell has all the characteristics of the card associated with it. Each activated ability that’s on the stack has the text of the ability that created it, and no other characteristics. The controller of a spell is the player who played the spell. The controller of an activated ability is the player who played the ability.
409.1b If the spell or ability is modal (uses the phrase”Choose one -” or”[specified player] chooses one -“), the player announces the mode choice. If the spell or ability has a variable mana cost (indicated by {oX}) or some other variable cost, the player announces the value of that variable at this time. If the spell or ability has alternative, additional, or other special costs (such as buyback or kicker costs), the player announces his or her intentions to pay any or all of those costs (see rule 409.1f). You can’t apply two alternative methods of playing or two alternative costs to a single spell or ability. Previously made choices (such as choosing to play a spell with flashback from his or her graveyard or choosing to play a creature with morph face down) may restrict the player’s options when making these choices.
409.1c If the spell or ability requires any targets, the player first announces how many targets he or she will choose (if the spell or ability has a variable number of targets), then announces the targets themselves. A spell or ability can’t be played unless the required number of legal targets are chosen. The same target can’t be chosen multiple times.
409.1d If the spell or ability targets one or more targets only if an alternative, additional, or special cost (such as a buyback or kicker cost) is paid for it, or if a particular mode is chosen for it, its controller chooses those targets only if he or she announced the intention to pay that cost or chose that mode. Otherwise, the spell or ability is played as though it did not have those targets.
409.1e If the spell or ability affects several targets in different ways, the player announces how it will affect each target. If the spell or ability requires the player to divide or distribute an effect (such as damage or counters) among one or more targets, or any number of untargeted objects or players, the player announces the division. Each of these targets, objects, or players must receive at least one of whatever is being divided.
409.1f The player determines the total cost of the spell or ability. Usually this is just the mana cost (for spells) or activation cost (for abilities). Some cards list additional or alternative costs in their text, and some effects may increase or reduce the cost to pay. Costs may include paying mana, tapping permanents, sacrificing permanents, discarding cards, and so on. The total cost is the mana cost, activation cost, or alternative cost, plus all cost increases and minus all cost reductions. Once the total cost is determined, it becomes”locked in.” If effects would change the total cost after this time, they have no effect.
409.1g If the total cost includes a mana payment, the player then has a chance to play mana abilities (see rule 411,”Playing Mana Abilities”). Mana abilities must be played before costs are paid.
409.1h The player pays the total cost in any order. Partial payments are not allowed.
Example: You play Death Bomb, which costs {o3}{oB} and has an additional cost of sacrificing a creature. You sacrifice Thunderscape Familiar, whose effect makes your black spells cost {o1} less to play. Because a spell’s total cost is”locked in” before payments are actually made, you pay {o2}{oB}, not {o3}{oB}, even though you’re sacrificing the Familiar.
409.1i Once the steps described in 409.1a-409.1h are completed, the spell or ability becomes played. Any abilities that trigger on a spell or ability being played or put onto the stack trigger at this time. The spell or ability’s controller gets priority.
Yes, this is a lot to digest. So I’m going to go over it one step at a time. For the purposes of not having to type the phrase a bazillion times, I’m going to shorten the phrase”spell or ability” to SoA.
Rule 409.a says that the first part of announcing your SoA is to put it on the stack. This is necessary so everyone can see the relevant portions of the SoA in order to verify that it is played properly.
The next step is to define the variables. This is not the same as choosing targets; that’s done later. The reason targets are chosen later is because the choices you make now may decide how many targets the spell has or what types of targets are legal.
The variables defined at this point are:
1. Choosing the mode of a modal SoA (or the”choose both” of Entwine)
2. Choosing whether to use any additional or alternative play costs. In some cases, such as Flashback and Morph, the only reason you’re allowed to play the SoA the way you are is because you’re doing it from an alternative cost. Note that you can’t pay multiple alternative costs. So you can’t play a creature with Morph face down and use Aluren to avoid paying the Morph cost.
3. Choosing the value of X in a mana cost. If you are using an alternative payment method, such as a Panoptic Mirror, the only choice you can make for X is zero. This means that Ertai’s Meddling, which says X can’t be zero, can’t be played from a Panoptic Mirror.
Now you choose the target or targets. Keep in mind that the choices made earlier were done so specifically so we know how many targets there are and what types they need to be. Take Falling Timber as an example:
Falling Timber
{2}{G}
Instant
Kicker–Sacrifice a land. (You may sacrifice a land in addition to any other costs as you play this spell.)
Prevent all combat damage target creature would deal this turn. If the kicker cost was paid, prevent all combat damage another target creature would deal this turn.
First you choose whether or not to pay the Kicker. (You don’t have to sacrifice the land just yet). If you chose to pay the Kicker, you then choose two targets for this spell; otherwise you only choose one. For purposes of spells such as Shunt, which target a”spell with a single target”, this choice determines whether Shunt can legally target it.
If the SoA does variable things to its targets, or if you can choose how the SoA divides or distributes its effect among the targets, you make that choice now. In the case of dividing or distributing, each target must get at least one of whatever there is; therefore you can’t choose more targets than there are things to hand out.
Wurmskin Forger
{5}{G}{G}
Creature — Elf Warrior
2/2
When Wurmskin Forger comes into play, distribute three +1/+1 counters among any number of target creatures.
Even though this ability says it can target”any number” of target creatures, the division rule limits you to three.
Now that you have done all this, you can then find out how much you need to pay for the SoA. All the choices from before factor into this calculation. If you are using an alternative cost, start with it, otherwise use the base mana cost of the SoA. To this, add anything that adds costs (such as Entwine costs if you chose to use it). Then subtract things that reduce the cost, such as Affinity reductions. (Note that a cost reducer can only reduce the costs written in the same form as what it expects, therefore Broodstar can never cost less to play than {U} {U} by applying Affinity, and Edgewalker reduces a Cabal Archon’s play cost to {2}, not {1}.
Once you have determined what it costs you to play this SoA, it’s locked in and nothing you do changes it, even if it would have changed the final result had it happened earlier. Now you can play mana abilities. You can’t pay any costs until you have all the mana in the pool you are going to need. Once you do, however, you can then pay the costs in any order. At this point, the SoA is considered played, and the player who played it can either play another ability or pass.
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