Rule 201.4a

If a player is instructed to choose a card name with certain characteristics, the player must choose the name of a card whose Oracle text matches those characteristics. (See rule 108.1.) Example: Dispossess reads, in part, “Choose an artifact card name.” The player can choose the name of any artifact card, even one that’s not legal in the format of the current game. The player can’t choose Island, even if an Island on the battlefield has been turned into artifact by some effect.