 As the material for these manuals was apparently derived from scholarly magical and religious texts from a variety of sources in many languages, the scholars who studied these texts likely manufactured their own aggregate sourcebook and manual with which to work spells or magic.In the notebooks of Leonardo da Vinci, it is stated that "Of all human opinions that is to be reputed the most foolish which deals with the belief in Necromancy, the sister of Alchemy, which gives birth to simple and natural things.