When studying magic, it is important to note that it follows The Rule of Three; all magic must come in three parts. Rituals are Incantation, Runes, and Components. Spells are Incantation, Movement, and Intent. Magic itself is composed of "Physical", "Natural", and "Soul", or magic from your physical body, magic from your surroundings, and magic from your life force, or magical core. The Unforgivable Curses can access each of the three aspects. The Imperius controls your body, the Cruciatus causes immense pain by causing the air around your to become electricity, and the Killing Curse breaks your connection to your core, killing all those who come into contact with it. This also means that Mundanes and Magic-Born Mundanes do in fact have some small amount of magic, as it is required to live. This may explain how rituals have a small amount of success when used by Mundane Wiccans. Our current magical society seems to only have access to the magic in our cores, though it can be assumed that there were or are cultures that can use the other two portions of magic. Where these cultures are, or if they could even exist on Earth is a topic worth looking into, however it could be decades before any conclusive results on the topic are published. It is rumored that certain highly powerful figures could access more than one of these aspects, Myrddin Emrys, Albus Dumbledore, and other signifigant persons being among the number of likely suspects. How such a phenomena occurs is still unknown, but it is highly unlikely that any such figures are willing to be experiememted on. There are also rumors that a Light warrior from the Wizarding Wars of the 1900's, notably the First or Second Voldemort Wars, wrote a book on how he discovered his powers, but if it does exist, it's most likely a valued and secret part of a family library. Whether that family wrote it originally or not could also be called into question, as some notable families claimed the large pureblood libraries as their own during the 2050's after pureblood crimes were finally exposed by the vigilante Bás.
An exerpt taken from an article by Violet Bones, written in Britian in the year 2198.
