 The 18th century Vilna Gaon was one of the most influential Rabbinic authorities since the Middle Ages; although he is counted among the Acharonim, he is held by many authorities after him as belonging to the Rishonim.Kabbalah tends to support the Halachic notion of the Descent of the Generations, by relating it to a metaphysical structure of descending levels of souls in each subsequent generation.Through processes such as Gilgul (Reincarnation), all souls are held to derive from the original collective soul of Adam.