The Mystical Trinity: Unraveling the Arcane
One day I was looking up esoteric and metaphysical stuff, when I got the idea of applying those real life concepts to Runeterra. I know Runeterra is a fantasy setting but it still gets influenced by real life concepts like Asian culture for Ionia, discrimination in Demacia, existence of religion and cults etc., so I decided to apply the idea of Body, Mind and Soul Trinity to Runeterra's magic system. Currently there exist three main "pure" types of magic: Celestial, Elemental and Spiritual. They are combined to created other types of magic like how Celestial and Elemental gives existence to Runic magic. Celestial is under the Mind aka the perception of the ideal world Spiritual is under the Soul aka the perception of the personal world and Elemental is under the Body aka the perception of the material world
Casting spells is using those different perceptions of the world to interact with reality. Each of those 3 types allows the magic user to interact reality with detailed and specific perception of the world. Elemental magic is the magic of the material realm, so any process governed by physical laws (and matter) can be influenced by it. Celestial Magic is drawing power from ideals/concepts unfiltered by bias thus it needs a conduit to act on the world with Elemental Magic being the fitting one as Elemental Magic governs the process of physical laws allowing ideals/concepts to manifest. Spiritual Magic takes the power granted by ideas and personal perception of existing things in the world. Those explanations make it easier to see the connections between Body, Mind and Soul with the 3 magic types of Runeterra. It's 1:1 equal as the Body, Mind and Soul are a broader, more vague and less defined, which means Elemental is a subclass of the Body, Celestial as the subclass of the Mind and Spiritual as the subclass of the Soul.
Using these three theoretical terms for a broader magical types, we can explain unknown arcane magics: Illusion/Deception magic would be the interaction between Mind and Soul as you see the concept [mind] and reshape its spiritual perception [soul] ergo the affected will perceive concepts of the world differently due to the interaction of the magic user. Don't confuse it with Illusion magic being a Celestial + Spiritual hybrid magic. It's more like you tap into less defined aspects of each type to alter the world. It would be logical for the idea of a Body, Mind and Soul trinity to exist in Runeterra as a concept and be used to explain things in the world, most likely as one of many ways on how magic works. The existence of the aforementioned concept would also make it way easier to explain certain unique types of magics. In the end though this is all a wacky hypothetical idea.