Philosophical Magic
Or, Mythology as Science Fiction for Pre-Modern Physics
In Fantasy we often want to explore some variation of the question, "what if some aspect of mythology or esotericism were real?" Perhaps the prototypical example is "what if magic actually worked?" Now, the exploration of this question may or may not be the real thrust of the work. The Lord of the Rings is hardly about Gandalf's ability to shoot light beams at wraiths and how that ability works. Indeed, for some Fantasy stories, the magical aspects of the world are simply there for decoration; the plot would work equally well in any number of settings even if the story overall would be less enjoyable for it. In these types of stories, fantastic elements often behave in such a way that the narrative is furthered by their behaviour. There is nothing wrong with this in itself, but trying to formulate consistent rules to describe the behaviour of the fantastic elements post hoc can be very difficult, with the rules usually becoming implausibly elaborate to avoid inconsistency. This runs very contrary to our intuition, as modern people, about how reality works; we often view the world in a reductionist way, with complex entities such as kingdoms and people emerging from very simple physical laws such as gravity and electrostatic repulsion.
Before modern times, people did not in general construe the universe this way. This results in a real difficulty if we want to create a conceptually parsimonious fantasy world which takes inspiration from mythology or historical forms of esotericsm. To pick an example, suppose we want to have in our universe a magic spell for turning a carriage into a pumpkin. But this really is incredibly difficult; problems like the differing mass of the carriage and the pumpkin pale in comparison to the fact that there is utterly nothing in our modern science to suggest that the universe should recognize the concepts of "pumpkins" or "carriages" as opposed to collections of atoms. Really, the universe does not, as far as we can tell, even recognize the pumpkin as being separate from the ground on which it rests or, for that matter, the air which surrounds it; the fact that we have a conceptual separation reflects the fact that we can, say, pick up the pumpkin from off the ground, a fact which simply arises from which chemical species the molecules of the bottom of the pumpkin and the molecules of the top of the ground are made of, and the consequent lack of chemical bonds or other forces between them that cannot be overcome by the simple effort of lifting the pumpkin. But many people in history, and even many unlearned people today, do have a model of reality in which the universe recognizes pumpkins and carriages, besides many other sorts of things like numbers, which is why, I suppose, some people still believe in numerology.
This really is the default sort of reasoning, though, if you aren't part of a culture that has worked out Maxwell's equations, atomic theory, and whatnot. A model of reality based on human concepts (pumpkins and carriages) rather than modern physical concepts (quarks and photons and so forth) is quite sufficient for categorizing practical human knowledge - when to plant your pumpkin crop and how to build carriages - and such models served us well for a very long time. They are just fine for storing most kinds of empirical knowledge. The problem arises when we speculate from these models - Fantasy is essentially Science Fiction based on a model of reality that is, from the modern point of view, conceptually upside-down; one where higher realms of reality, the intellectual or celestial, impart behaviour and significance to the material world, instead of more sophisticated concepts emerging from the operation of the simple physical rules of the material world. Speculations from the upside-down models of most pre-modern thought end up postulating physical rules like "saying these magic words will turn a pumpkin into a carriage" that seem incredibly improbable to someone using a modern world-model where pumpkins and carriages are just arbitrary designations for collections of atoms and words are just arbitrary symbols used by humans to communicate. This problem with magic words and rituals was in fact noted by scholars in the Renaissance, when they began to understand words and writing as symbols only, without inherent power. The sceptics were divided about the implication - that ritual magic did not work, or that the effects of ritual magic were accomplished through the agency of non-human intelligences who understood the symbolism, typically thought to be angels or demons.
Although other explanations are possible - our reductionist universe is not the only thing logically possible - after long consideration, I think that this explanation, that complex magic arises through the mediation of an intelligence, is the most satisfactory. Alternatives require a universe with pre-modern conceptualization, which is simply too awkward for this modern person to work within creatively. It allows magical phenomena consistent with traditional stories and lore, while also allowing these to be based on simple laws that integrate well with modern conceptualizations of physics, and allow physico-magical phenomena to emerge from their interaction. Of course, it is perhaps preferable that the mediating intelligences not actually be much like angels or demons for a variety of reasons, chiefly that such super-human beings would be difficult to portray realistically and would probably impose their own personalities and moral agendas, making the use of magic more a social act of supplication than the dependable, repeatable procedure usually desired for Fantasy settings. That being said, it is perhaps best from the point-of-view of storytelling, that the nature of the intelligence involved be ambiguous: does it even have a will of its own or is it a mere echo of the magician's own volition? Is it mechanical or divine? Has it a moral agenda, good or evil? It is interesting to leave those questions for the characters to discover, even if theoretical considerations insist that some form of intelligence must interpret the symbols and objects of magic.
Implementing this kind of internally consistent "hard fantasy" has been a real challenge. I hope you will find the Philosophical Magic campaign interesting.