The Sword of Illusion can only be activated by an Illusionist Wizard, or by a spell caster who knows at least one spell per level from the school of Illusion.
The Sword of Illusion can only be activated by someone who has Illusion as a primary school, or by a member of a class or prestige class which is based on illusion. It may also be activated by a spontaneous caster who can cast at least one spell per level from the Illusion school.