Declaration of Naught — ruling 1

You can name either half of a split card, but not both. If a player casts the half with the chosen name, it can be targeted by the second ability. In addition, if a player casts a fused split spell with the chosen name, it can be targeted by the second ability.

Declaration of Naught : règles, fonctionnement et interactions (MTG)

Declaration of Naught is one of those cards players keep asking about. Here is, in plain words, what its official text says, the rulings published by Wizards of the Coast, and the combos players actually run.

Official card text

As this enchantment enters, choose a card name. : Counter target spell with the chosen name.

How it works : Declaration of Naught

Original English text — Wizards of the Coast / Scryfall

#1April 1, 2008· Wizards of the Coast
You can name either half of a split card, but not both. If a player casts the half with the chosen name, it can be targeted by the second ability. In addition, if a player casts a fused split spell with the chosen name, it can be targeted by the second ability.
No other card is named in this ruling.