Natural magic works with materials rare in Europe but common in and around India.
Some substances, however, are presumably available domestically. Magicians kill
animals when they are in heat, for example, hoping to extract powerful love potions from
their bodies. William cites Pliny’s example of the fish called echineis or remora that can
cause a ship to cease moving, and he tells how the gem and herb called heliotrope can
make a person invisible. He includes under the heading of natural magic what he calls the
sensus naturae, which corresponds roughly to extrasensory perception (by which a
woman can detect her beloved when he is two miles away, or a dog can identify a thief
amid a crowd).
William holds that natural magic is in itself harmless; indeed, God should be glorified
for such wonders. Yet it can be used for illicit ends, and in early Christianity it was
condemned because it seemed to involve the work of gods and thus led people into
idolatry. More fundamentally, he holds that many techniques ascribed to natural magic
cannot in fact work unless demons intervene: images, characters, and incantations have
no effect in themselves, and if they have efficacy it is only as signals to demons. Words
can work only by means of their material (air), their form (sound), or their signification,
and William discounts all these possible explanations for the natural efficacy of
incantations; air, for example, can kill people only if it is infected with venom from toads,
dragons, or plague. (He does grant that names of God seem to have exceptional efficacy,
although he says the magicians use a corrupt substitute for the Tetragrammaton.)
Furthermore, William disputes many claims about magic and says that if magic were
as powerful as some have claimed any magician could hold the world at his mercy. Yet
his skepticism is at times tempered by recollection of the wonders natural magic can
accomplish. He doubts that mercury is effective against demons and incantations, until he
recalls that a crab suspended in the air deters underground moles and that peony expels
demons from possessed people.
Yet many of the pretended accomplishments of magic are mere trickery, exemplified
by the use of magic candles that can make a house appear to be filled with serpents, and
by illusions comparable with fantastic dreams. Demons often use trickery, as well as the
occult powers in nature, in aiding magicians; thus, the demonic entourage produced by
“Major Circle” is merely an illusion, seen only by those inside the magic circle, and the
horses that appear leave no hoofprints. Practitioners of natural magic sometimes also
deceive people with mere illusions.
Thomas Aquinas discussed magic in various places but most importantly in Summa
contra gentiles 3.101–05. He tells how magicians make use of herbs and other objects,
verbal formulae, figures and characters, images, sacrifices, and astrological observations
to discover hidden treasure, foretell the future, open doors, become invisible. Yet he
believes the means employed are not a sufficient cause for the effects attained, which
require the intervention of demons. The magicians are typically criminal persons using
these arts to perform such offenses as adultery, theft, and murder. Elsewhere, however,
Thomas deals with the occult virtues in nature in a way that is less hostile and examines
the ways in which astral influences can underlie such virtues. While he does not speak of
the use of these occult virtues as “natural magic,” as other writers did, he manifests an
interest in such phenomena and a willingness to acknowledge that many extraordinary
effects could be accomplished by means within the natural order.
Medieval france: an encyclopedia 1090