There are certain items that can be enchanted even though they already have an enchantment. The Law of the Firsts states that once an item is enchanted, it can not be enchanted again and can not accept another enchantment. The act of enchanting requires an item with no existing enchantments, a filled soul gem, knowledge of an enchantment, and the use of an arcane enchanter. 'Don't suppose you'd enchant my sword? Dull old blade could barely cut butter.' ― Hold Guard
