In plain English, how does casting spells and using creature abilities work with the stack and priority?

Question

I'm a relatively new player to Magic: the Gathering. I was reading the expanded rules to try to understand exactly when it's okay to cast instants (e.g. Cancel) and use some abilities (e.g. Goblin Diplomats should be tappable sometime during other peoples' turns), but I don't seem to be making much progress: as I come to understand some things, others make less sense.

My confusion is boundless

For instance: to cast Instants one needs priority. Spells go on the stack, and priority gets passed at some points (I have no idea when), and effects on the stack are resolved when both players have passed priority. But when is that? I can't find any mention of when the other player gets the priority to cast an instant, except on their own turn. Furthermore, The Complete Turn states that during the Main Phase:

505.4. Second, the active player gets priority. Players may cast spells and activate abilities. The active player may play a land.

So players (plural) may cast spells, but only the active player has priority, so only the active player can cast an instant. The turn rules, and the rules on Casting Spells, never mention any point at which the other player gets priority, so when can they possibly Cancel?

In addition, you can only cast a spell when the stack is empty, so the entire stack must be able to be resolved in your turn at some point.

I need an explanation!

I could go on a bit more. There is also Counterflux which can be overloaded to "Counter each spell you don't control", which seems like it could only possibly work with an understanding of the stack.

Could someone explain, in simple English:

• When can Instants be cast?
• When can tap abilities be used?
• What do Instants and abilities have to do with the Stack and Priority?

Answer 1

I am going to reiterate that the Basic Rules are sufficient for and a better way to learn how to play MtG rather than the Comprehensive Rules

When can Instants be cast?

Instants can be cast on your own turn, during your opponents turn, and in response to other spells. This differs from Sorcery cards, which can only be cast during your own Main Phase. (MtG Basic Rules, Page 6)

Instant - An instant is just like a sorcery, except you can cast it just about any time you want, even during your opponent’s turn or in response to another spell. Like a sorcery, an instant has its effect, then you put it into your graveyard.

When can creatures use their abilities, like tap abilities?

Anytime you could cast an Instant. There is nothing inherently different between an activated ability with the tap symbol in its cost and other activated abilities and their costs. Tapping is a cost, and just like any other cost, it must be paid before activating an ability.

Activated Abilities - An activated ability is an ability that you can activate whenever you want, as long as you can pay the cost. [...] Each activated ability has a cost, then a colon (“:”), then an effect. [...] Some activated abilities contain the {T} symbol in their costs. This means that you must tap the permanent to activate the ability. You can’t activate the ability if the permanent is already tapped. (MtG Basic Rules, Page 12)

Creature - [...] Unlike other types of permanents, creatures enter the battlefield with “summoning sickness”: a creature can’t attack, or use an ability that has {T} in its cost, until it has started your turn on the battlefield under your control. You can block with a creature or activate its other abilities no matter how long it’s been on the battlefield.(MtG Basic Rules, Page 6)

What do Instants and abilities have to do with the Stack and Priority?

Instants, Activated Abilities both go on the stack. The stack gives players the opportunity to respond to spells/abilities before they resolve. The stack is a First In Last Out (FILO) zone, where spells and abilities exist until they resolve or are countered. (Instants/Sorcery) spells have their effect and then go to the Graveyard, (Creatures/Enchantments/Artifacts/Planeswalkers) resolve and become permanents on the Battlefield, (Triggered Abilities/Activated Abilities) are not represented by a physical card, so they resolve and disappear into the AEther.

Priority is just the way MtG is designed to handle whose turn it is to do something. Players can cast Instants or activate abilities on other players turns, so the game needs a way to determine who goes first.

The Stack - Spells and abilities exist on the stack. They wait there to resolve until both players choose not to cast any new spells or activate any new abilities. Then the last spell or ability that was put onto the stack resolves, and players get a chance to cast spells and activate abilities again. (You’ll learn more about casting spells and activating abilities in the next section.) This zone is shared by both players.(MtG Basic Rules, Page 8)

Priority - Since players can cast instants and activate abilities during each other’s turns, the game needs a system that makes sure only one player can do something at a time. Priority determines, at any given time, which player can cast a spell or activate an activated ability.

The active player (the player whose turn it is) gets priority at the beginning of each step and each main phase—except for the untap step and the cleanup step. When you get priority, you can cast a spell, activate an activated ability, or pass (choose to do nothing). If you do something, you keep priority, so you make the same choice again. If you pass, your opponent gets priority, so now he or she gets that choice. This goes back and forth until both players pass in a row.

When both players pass in a row, if there’s a spell or ability waiting on the stack, it resolves. Then the active player gets priority again, and the system repeats. When both players pass in a row, if there’s no spell or ability waiting on the stack, that part of the turn ends and the next one begins.(MtG Basic Rules, Page 30)

Answer 2

Basically, the answer to this question lies in the understanding of the phases of the turn.

there are a number of phases and steps that a turn goes through, here is a brief overview:

1. Untap step
2. Upkeep
3. Draw step
4. First Main Phase
5. Combat phase (has many sub steps, skipped for understanding)
6. Second main phase
7. End step
8. Cleanup.

The above is not an exhaustive list, but it gives you enough understanding to get your head around what's going on.

Whoever's turn it is, that player is the Active Player. The other player(s) are Non-Active Players. This terminology will help with explaining things.

The best rule of thumb is "The active player has priority right now." 90% of the game this will be true. and during this time you can't do anything. To clarify a little, Whenever a new phase or step begins, the active player has priority. Think of it this way, the active player moves into their main phase, they have lands to play and spells (including creatures) to cast, and this is where that process all starts.

The next thing to understand is how the stack works. Again, a good rule of thumb is "if something happens, it usually uses the stack". For example, casting a creature uses the stack, activating Olivia Voldaren's ability uses the stack. Casting Oblivion Ring uses the stack, so does it's enter the battlefield trigger (there are numerous answers about these for further information) essentially, anything that doesn't directly generate mana uses the stack. I say directly, because Scalding Tarn's ability will get you mana after it resolves, but it does not generate mana and DOES use the stack.

Here is what happens with the stack:

1. Someone puts something onto the stack
2. That player gets priority and could cast additional spells if they wish.
3. After that player passes priority, each subsequent player gets priority.
4. After all players pass priority, the object on the stack resolves.

When a player has priority with something on the stack, they can cast instants (or spells with flash)

if someone chooses to cast something with something else on the stack, then the whole process repeats for THAT ITEM until it has resolved, and then steps 2-4 are repeated for the Original item.

let's look at an example:

Albert is in his main phase, he casts Ancestral Recall. Oh no! Nancy is wisely playing islands, and with Counterspell in hand, wants to tap 2 of them to make sure Albert's day is ruined.

Here is how this looks on the stack:

  1. Albert casts Ancestral Recall. Ancestral Recall Goes onto the stack.

     2. Albert wants to do nothing and implicitly (by sitting there doing nothing) passes priority.

     3. Nancy gains priority and responds with Counterspell.

        4. Nancy gains priority and implicitly passes by doing nothing.

        5. Albert gains priority and, looking smug, says "In response" and slaps his own Counterspell onto the table. Poor Nancy!

Uh oh, things are getting complicated now! Here's a look at the stack right now:

Albert's Counterspell

Nancy's Counterspell

Albert's Ancestral Recall

        6. Albert gains priority again, and again silently does nothing.

        7. Nancy doesn't have anything else to do so she disappointedly says "Resolves."

     8. Albert's counterspell resolves.

     9. Nancy's counterspell is removed from the stack, so we skip back down to just looking at Albert's Ancestral Recall.

  10. Crossing his fingers, Albert passes priority.

  11. Grumpily, Nancy says "Resolves." She has no more answers.

  12. Albert's Ancestral Recall resolves. He cackles maniacally as he draws 3 additional cards.

This demonstrates how things work with the stack. This passing of priority happens everywhere. If Albert wants to go to the combat phase, he passes priority and Nancy might do something in his main phase. If Albert wants to end his turn, Nancy gets an opportunity to cast some spells before her turn starts.

hopefully this has helped understand the stack, in answer to your bullet points:

1. Instants can be cast at any point where you have priority, all required targets and no restrictions prevent you casting them (e.g. you can't cast Doom Blade with no creatures on the battlefield, and you can't cast anything after Silence resolves).
2. Tap abilities can be used any time you can cast an instant, excepting abilities that state otherwise (such as Birthing Pod's). Remember that creature have "summoning sickness" (creatures that you haven't controlled since the beginning of your turn may not activate abilities with the Tap or Untap symbol unless they have haste).
3. Instants and abilities are put onto the stack to resolve, and can only be placed there by the player who has priority. Hopefully the above has explained when this happens.

Most of the time, priority passing happens fluidly and implicitly. As a result, usually it is enough to know that "in response" means that the spell is still on the stack, and you get to do things if you want at the end of each part of the turn.

Here is an interesting situation with how the stacks and priority work to show how you can't do whatever you want, whenever you want.

1. Alberta casts Lingering Souls, a powerhouse of a card against Norman's deck, and passes priority.
2. Norman has a Surgical Extraction in hand and wants to use it to stop the spell being flashed back and clear the other copies away to limit the damage, but the spell is on the stack so he cant exile it yet, he passes priority and the spell resolves.
3. Norman wants to cast Surgical Extraction, but since the spell resolved, priority reverts to Alberta. He has to wait until Alberta moves to a different phase or casts some other spell to get priority.
4. Alberta gets greedy and fancies 2 more tokens, she flashes back Lingering Souls straight away. Poor Norman's Surgical Extraction is now a dead card. The Lingering Souls is on the stack and will then be exiled.

There are times where priority has a massive impact, and the above is one of them.

Answer 3

I will not answer any of your (somewhat) specific questions, as I feel they would not clear up much of the confusion you seem to be feeling. Instead let me give some general advice.

This document is designed for people who've moved beyond the basics of the Magic: The Gathering(R) game. If you're a beginning Magic(TM) player, you'll probably find these rules intimidating. They're intended to be the ultimate authority for the game, and you won't usually need to refer to them except in specific cases or during competitive games.

That is the first line of the expanded rules that you linked to, and you should not ignore it.

Reading the Comprehensive Rules is a terrible way of learning the basics of the game. Absolutely dreadful. I would have given up on the game long before I've played my first match if I first had to read and understand that brick, even though it was smaller back then. It's like studying quantum chemistry in order to cook a pack of instant noodles. I cannot stress this enough: Don't read the CompRules to learn the game. Only open the CompRules if you have a very specific question and are already familiar with the basic rules.

Instead you have 2 much better options:

Find a group of friendly, experienced players who are willing to play casual games with you, who can explain the basics, point out your mistakes, and let you take back moves, maybe even play with open hands. Or, if you feel more comfortable reading, read the basic rules by WotC.

That's really all there is to say. Don't get ahead of yourself, it will only frustrate you.

Answer 4

I think what answers most of your confusion is section 117 of the comprehensive rules, the section on timing and priority. Most specifically the rules that deal with who has priority and how it is passed, 117.3, and how priority passing affects spells and steps of the game, 117.4.

117.3 Which player has priority is determined by the following rules:

117.3a The active player receives priority at the beginning of most steps and phases, after any turn-based actions (such as drawing a card during the draw step; see rule 703) have been dealt with and abilities that trigger at the beginning of that phase or step have been put on the stack. No player receives priority during the untap step. Players usually don’t get priority during the cleanup step (see rule 514.3).

117.3b The active player receives priority after a spell or ability (other than a mana ability) resolves.

117.3c If a player has priority when they cast a spell, activate an ability, or take a special action, that player receives priority afterward.

117.3d If a player has priority and chooses not to take any actions, that player passes. If any mana is in that player’s mana pool, they announce what mana is there. Then the next player in turn order receives priority.

117.4 If all players pass in succession (that is, if all players pass without taking any actions in between passing), the spell or ability on top of the stack resolves or, if the stack is empty, the phase or step ends.

In plain English:

117.3a and 117.3b: Priority resets to the player who's turn it is when something resolves and as the game proceeds through the turn.

117.3c: After a player with priority casts a spell or activates an ability, putting it on the stack, they keep priority.

117.3d: When the player who has priority decides not to do anything with it, priority passes.

117.4: If everyone passes priority, the last spell or ability put on the stack resolves, or the game moves to the next step of the turn if there's nothing on the stack.