Universals are a concept in metaphysics that deals with the nature of abstract objects. The Problem of Universals concerns whether universals exist in reality or are simply mental constructs. One famous argument for the existence of universals is Plato's theory of Forms. Plato believed that there is a transcendent realm of perfect Forms, of which physical objects in the world are merely imperfect copies. On the other hand, nominalists argue that universals do not exist independently of individual objects. Instead, they are just general concepts that we use to group similar things together. For example, the concept of redness is just a way for us to categorize objects that share the property of being red. The debate over the existence of universals continues to be a central issue in metaphysics, with philosophers offering various arguments for and against their existence. Some believe that universals are necessary for explaining the similarities between objects, while others argue that they are unnecessary and add unnecessary complexity to our understanding of the world. Ultimately, the debate over universals raises important questions about the nature of reality and how we categorize and understand the world around us.