The Elder Scrolls III: Morrowind · Spellmaking restriction
Custom effect prerequisites
A custom spell’s effect availability depends on buying a base spell with that effect; the guide says 19 effects cannot be used in custom spellmaking.
How it works
Base spells are spells bought from spell merchants. The guide says a base spell containing the desired effect must be purchased before creating a custom spell with that effect. It also reports 141 separate magical effects across six spellcasting skills, with 19 unavailable for custom spellmaking; the cited introduction gives Vampirism as an example. These counts are the guide’s account.
Read the supporting references
Steam Community :: Guide :: The Arch-Mage's Handbook - A Practical Guide to Morrowind's Magic System
Check the edition and source version for patch-specific details. Guide methodology.