# Playing Cards - Costs and Memory

#### General Rules:

1. Reserve costs are paid by reserving cards into the memory zone from the hand.
   1. Cards selected for reserve costs may only be changed up until the player confirms the selection and places the activated card onto the Effects Stack.
   2. Players may not exchange reserved cards once this has been done and may not interchange already reserved cards while activating another card.
   3. Players must clearly represent chosen and reserved cards.
   4. Cards placed into memory for reserve costs remain there even if the card or effect does not resolve.
   5. Materialization can involve cards with reserve costs. In this case, reserve costs are paid rather than memory costs.
2. Memory costs require banishing cards from cards in the memory zone at random.
   1. Cards selected for memory costs are chosen randomly by a fair selection process (a process that provides equal probabilities for any one card to be selected).
   2. Once cards have been selected for memory costs (including cards with floating memory chosen for payment), no cards may be interchanged or reselected and the chosen cards are then banished simultaneously.
   3. The card is then immediately placed into the Effects Stack for resolution.
3. Cards without specified reserve costs can’t be paid for by reserving 0 cards; cards without memory costs can’t be paid for by paying a memory cost of 0. Not having a cost is not the same as having a cost of 0 in each of these respects; players can’t pay null/non-existent costs.

See [floating memory](/glossary/keywords-and-abilities.md#floating-memory) for additional information on cost payment methods.


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