Summary zu Dewarim 18:26

"A conjurer [chover chaver]" (Deuteronomy 18:11) is one who pronounces incantations, as explained in Sifrei (Shoftim 172). And all of these arts — divination, soothsaying, and augury — are all referred to by our sages of blessed memory as "the ways of the Emorites." Within the body of these practices, however, some are forbidden and some permitted. The Rambam's view on this is that anything not dictated by rational considerations is forbidden and anything else, permitted. This view is based on the statement in Tractate Sabbath (67a): "Abbaye and Rava both agree that anything within the province of healing is not in the category of 'the way of the Emorites.'" The implication is that anything dictated by reason is not within the category of "the ways of the Emorites" and that anything else is. This is the intent of the question which follows (Ibid): "Is this to imply that anything not within the province of healing is in the category of 'the ways of the Emorites'? Did we not learn: 'A tree that is losing its fruits should be coated with red paint and be weighted down by stones so as to weaken it [its over-richness being responsible for the fruit loss]'?" That is: we can understand weighing it down, this being dictated by reason, but what healing is effected by coating it with red paint? There are no cause and effect considerations or other natural considerations which would warrant this. And the Gemara answers: "So that people notice its condition and pray that it be healed."