All human cultures in some way have to deal with accounting for the myriad of objects and phenomena surrounding them. We live in a world of infinite objects that are constantly changing, yet even in this imposing world of objects and change, there seems to be an underlying unity and stability. For instance, every human being begins as an infant and then grows into an adult. Every adult is a different object than they were as an infantin fact, they are unrecognizable as being the same object. Yet we recognize that the are the same object , that something has remained the same even though the infant has changed into an object that is nowhere close to its original state. Likewise a corpse is nothing like the original living human being, but we still recognize that something has remained constant. We can see the same stability and constancy even across objects. While the world is full of trees, there is still some constancy and stability to "treeness" which never seems to change.
This observation of the world of phenomena leads many cultures to believe that the infinity of things and their changes can ultimately be related back to a single object, material, or idea. The problem of finding the one thing that lies behind all things in the universe is called the problem of the one and the many. Basically stated, the problem of the one and the many begins from the assumption that the universe is one thing. Because it is one thing, there must be one, unifying aspect behind everything. This aspect could be material, such as water, or air, or atoms. It could be an idea, such as number, or "mind." It could be divine, such as the Christian concept of God or the Chinese concept of Shang-ti, the "Lord on High." The problem, of course, is figuring out what that one, unifying idea is.