Spell/Miracle Memory is a gameplay mechanic in Demon's Souls. It is separated into two aspects: Spell Memory and Miracle Memory.
Both are a measure of how many spells or miracles the player can have ready to cast at one time, with Spell Memory affecting spells and Miracle Memory affecting miracles. Respectively, they can be increased by levelling up Intelligence and Faith. A character cannot learn spells without at least 10 Intelligence, which is to say, Sage Freke and Freke's Apprentice will refuse to sell spells to a character with less than that; likewise, a character cannot learn miracles without at least 10 Faith. They are independent of each other, in that the player is not limited to certain number of currently memorized spells/miracles except by the maximum number of either the player is able to memorize at one time.