Psionics are manifested purely by mental discipline. Psionics were originally introduced in the original "Dungeons & Dragons" Supplement III – "Eldritch Wizardry". Psionics have appeared in all editions; however, they are only part of the core rules in "Advanced Dungeons & Dragons" 1st edition. In 2nd, 3rd and 3.5 editions, psionics are divided into five or six disciplines, or groupings of powers. In 2nd edition, Psionicists gradually gain access to additional disciplines as they advance in level. In 3.5 edition, several psionic character classes are forced to choose one of them, thereby losing access to the most potent powers of the others. In 2nd edition, each power is tied to an ability score (generally Constitution, Intelligence or Wisdom); in 3rd edition, each discipline is tied to an ability score; and in 3.5 edition, all powers use the same ability score: either Intelligence, Wisdom, or Charisma depending on the manifester's class.