Let's take again an imaginary world where, without its inhabitants realizing it, everything is physically influenced by what people thinks, by what they believe, by how they see the world. This world is more or less in a medieval stasis because the majority of people received no form of education outside home-schooling, so there is no common knowledge of physical laws upon which to build complex machinery. Every attempt to advance technology, except very small and gradual ones, usually fails.
Magic, instead, exists.
But there is a problem: if the majority of people received no form of education outside home-schooling of course there also is no common knowledge of magical laws upon which to build complex spells. But magic exists because legends are full of magical creatures and supernatural events, so people are more inclined to believe in magic than in machinery able to plow their fields. So I'd like to define some rules to solve this contradiction and make magic work, even if only under some strict conditions that practically prevent it to be commonly used.
Right now I defined something like that:
Magical popular belief that require none or few direct perception of its effect work without problems (i.e. hang some oak leaves outside your house to protect it from mischievous spirits). This is because there is nothing physical that should be altered by the belief, the magical effect just prevents the influence of something that doesn't physically exists to begin with and is generated by the same belief that prevent its effect from working.
Magical popular belief that influences physical things works only where the people that believe in it live, only if the huge majority of people believe in it, and the scale of its effect depends inversely on the direct contact those people have with the target of the magic. For example:
- A ritual to have a good harvest usually works because its effect manifests on the seeds, that are under the earth so the people are not seeing what happens, they don't know what should exactly happen and there is no risk to have a hundred of different people with different beliefs that look every day at those seeds and think that maybe it doesn't work because it's not what they expect.
- A magic healing potion works only if the one who made it is respected by the people as someone who is expert of healing potions. The direct contact with the sick person is usually restricted to only few people, so the belief in the healer who prepared the potion is much stronger than the direct perception of the effects of the illness (and anyway things like a wound closing does not happen when people are looking at the wound, but only where nobody is looking at it for a long time, i.e. overnight when people sleep).
- Popular belief cannot create miracles like pumpkins magically appearing mid-air during a famine, but maybe if they really really believe in the powers of a village elder something like a rain dance can bring rain after a couple of days after it's done (like in the previous case, clouds appear overnight when nobody can see them).
About wizards with spellbooks and staffs able to create fireballs out of thin air...well, the magic does not work as consistently as needed to have schools that teach magic, so they are very uncommon. Studying this kind of magic is long, frustrating and with very little results, so it can be done only by few wealthy people with love for knowledge and a lot of time to spare. Basically it works like this: first, the wizard must be recognized as a wizard and seen as a figure of power and authority, so they dress in a way that makes them recognized as such; second, their spells with their words and gestures and symbols have the objective of making ALL the people around the wizard recognize subconsciously the effect he wants to invoke (i.e. instilling the idea of fire) and require EXTREME precision; third, the mage has no control on what is generated by the belief of the people (for the fire it can be everything from a little spark to a huge flame) so he needs some item to transform whatever appears in what the spell is supposed to do (in the case of the spark some flammable powder); finally, when the spell effect has the shape the people expect to and is recognized as such, it works as a spell should. This is obviously easier when the wizard has a reputation but very hard and dangerous for a beginner, so it's usually safe for a wizard to build first its reputation with small and simple tricks.
Can those rules work or do you see some flaws? Any idea on how they can be fixed/extended? And in particular for the case of the wizard, the example of the fireball is easy, but I have serious problem to extend the same concept to other kinds of spells (i.e. manipulate wind, ice, trajectory of throwed items, etc.) without inventing natural stuff with unusual properties or breaking the technological rules that force the medieval stasis.