Magic, according to those who dwelt on such things came in two main flavours in the Middle Ages. Natural or occult magic was based on special properties of natural occuring things, for instance magical properties of certain herbs or animals etc, whereas demonic magic was specifically the summoning of spirits for evil.
Another page on my Stupor Mundi site published, this time looking at the subject of Magic! All the content here is taken from the book by Kieckhefer – its basically my notes of the examples he provides.
How magic was viewed in the Middle Ages is a fascinating subject. It was believed to be real and quite dangerous. Richard Kieckhefer’s book Magic in the Middle Ages is a brilliant introduction to the subject area and I recommend reading it. As well as introducing the background to belief, it also traces the classical, celtic and germanic background to magic in Western Europe, as well as looking at Arabic and Jewish sources. The development of a clerical underground and the developing persecution of witches is also covered.
For me however, the most useful aspect was just to get a reliable source of possible examples of how magic was practiced in the middle ages. I’m currently working on stories set in a historical context where the characters use, or attempt to use magic, so I found this book invaluable. Although it’s an academic text, it is not dry or dull at all.