Problem of universals

The problem of universals is a central question in metaphysics. Metaphysics is the branch of philosophy that studies the nature of reality. This specific problem asks about the status of shared properties. If two objects share a color or a shape, does that property exist independently?

Philosophers wonder if qualities like "redness" or "circularity" exist beyond the objects themselves. A universal is defined as a quality or a relation found in two or more entities. For example, if every cup holder is circular, circularity is a universal property. Universals help humans make mental connections between nonidentical objects. While philosophers agree we can think about universals, they disagree on their actual existence.

Ancient philosophers explored this through a process called predication. Predication involves using terms to describe the characteristics of a subject. In his work *Categories*, Aristotle explained this using universal and singular terms. A universal term, such as "man," can be predicated of many individuals. A singular term, such as "Callias," refers to only one specific person. This distinction helps organize how we describe the structure of the natural world. By studying these terms, thinkers attempt to understand the intelligible order of the world. This process is vital for logic and epistemology, which is the study of knowledge.

Plato and Aristotle offered very different views on these properties. Plato believed in a sharp distinction between two worlds. He argued that the world of perceivable objects is imperfect and changing. In contrast, he believed in a world of eternal Forms, or *eide*. For Plato, true knowledge only concerns these unchanging Forms. He viewed the sensible world as mere shadows of the real world of Forms. This view is known as Platonic realism. However, some critics, like Diogenes of Sinope, challenged this idea. Diogenes famously noted that he could see Plato's cups, but not "cupness."

Aristotle disagreed with his teacher, Plato, regarding the location of these forms. He transformed Plato's ideas into "formal causes." These are the essences or blueprints of individual things. Aristotle focused on the natural world and its many living beings. He believed that a universal is a part of the individual thing. For instance, an oak tree possesses "oakness" as part of its nature. This makes Aristotle a moderate realist. He believed we can gain knowledge of the sensible world through observation. This approach helped establish him as a founder of induction.

During the Middle Ages, the problem was introduced by the philosopher Boethius.

Boethius studied how universals relate to particulars. He argued that a universal must be present in each particular simultaneously. He also noted that a universal must be present in an identical manner. Boethius proposed that the human mind can abstract these qualities. The mind can separate a concept in thought even if it is not separate in reality. This allowed him to avoid the extremes of Platonic realism and pure mental construction. He suggested universals are the mind thinking about particulars in an abstract way.

Medieval philosophy saw a rise in both realism and nominalism. Realists like Thomas Aquinas and Duns Scotus argued for the reality of universals. Aquinas believed the essence and existence of a thing were distinct. Duns Scotus argued there is only a "formal distinction" between them. Scotus believed properties like redness exist as mind-independent entities. On the other hand, nominalists argued that universals are merely verbal constructs.

The philosopher Roscellinus claimed universals were just vocal utterances. William of Ockham was a prominent nominalist in the 14th century. He argued that universals are products of human thought and language. To Ockham, nothing outside the soul is truly universal.

In the 19th century, new perspectives emerged from different thinkers. Georg Wilhelm Friedrich Hegel proposed a dialectical relationship between universals and particulars. He suggested that one cannot exist without reference to the other. John Stuart Mill discussed how we identify objects by certain attributes. He noted that we might focus on attributes necessary to identify a man. Charles Sanders Peirce, the father of pragmatism, offered another view. He argued that if a mental fact works in practice, it functions as a universal. Peirce also believed that "Thirdness," or general laws, are extra-mental realities. These diverse views continue to shape how we understand the relationship between thought and the world.