Does a creature enchanted by Pacifism lose the ability to block or only the ability to attack?

Pacifism reads: 'Enchanted creature can't attack or block.' This is an explicit restriction on both combat actions, so the enchanted creature loses the ability to participate in either role during combat.

Under CR 508.1a, a creature can only be declared as an attacker if it is able to attack — any rule or effect that says a creature 'can't attack' prevents it from being declared in the declare attackers step. Similarly, CR 509.1a governs the declare blockers step, and a creature that 'can't block' cannot be declared as a blocker there either.

The word 'or' in Pacifism's text covers both restrictions simultaneously. Neither ability is preserved — the enchanted creature is locked out of both attacking and blocking for as long as Pacifism remains attached to it.

Example: Your opponent's 4/4 Bear is enchanted with your Pacifism. On their turn, they cannot declare the Bear as an attacker. On your turn, if you attack, they also cannot declare that Bear as a blocker. It is effectively frozen out of combat entirely.

This is consistent with CR 702.2c (defining 'can't attack or block' restrictions) and the general principle in CR 101.2 that if an effect says a creature can't do something, that restriction is absolute for its duration.