739.4.a. Whether or not a Game Object has Reaction is a characteristic of that Game Object and may be checked or referenced by other Game Effects.
739.4.b. Whether or not a Spell has Reaction is a characteristic of that Spell and may be checked or referenced by other Game Effects.
739.4.c. Whether or not an Ability has Reaction is a characteristic of that Ability and may be checked or referenced by other Game Effects.