In the beginning there were the Four Crystals, and together they formed one principle. Thus the world was created.
The Four Crystals then created humanity in their own image, and presided over their destinies.
The Crystal Principle is a mysterious force mentioned in Final Fantasy Crystal Chronicles: The Crystal Bearers. It is said to have created the four tribes: Lilty, Clavat, Selkie, and Yuke, along with their Tribal Crystals.
The Principle is the personification of, or at least helps maintain, the natural order of the world via the Tribal Crystals. If one of those is destroyed, the Tribe it controls vanishes, and the world plunders into chaos.