Problem of universals

In metaphysics, the problem of universals refers to the question of whether properties exist, and if so, what they are.Properties are qualities or relations that two or more entities have in common. The various kinds of properties, such as qualities and relations, are referred to as universals. For instance, one can imagine three cup holders on a table that have in common the quality of being circular or exemplifying circularity, or two daughters that have in common being the daughter of Frank. There are many such properties, such as being human, red, male or female, liquid, big or small, taller than, father of, etc.

While philosophers agree that human beings talk and think about properties, they disagree on whether these universals exist in reality or merely in thought and speech.

There are many philosophical positions regarding universals. Taking "beauty" as example, three positions are:

The main positions above are also called "extreme realism", "strong realism", and "anti-realism" respectively. A notable variant of anti-realism is nominalism.

The realist school claims that universals are real—they exist and are distinct from the particulars that instantiate them. There are various forms of realism. Two major forms are Platonic realism (universalia ante res) and Aristotelian realism (universalia in rebus).Platonic realism is the view that universals are real entities and they exist independent of particulars. Aristotelian realism, on the other hand, is the view that universals are real entities, but their existence is dependent on the particulars that exemplify them.

Realists tend to argue that universals must be posited as distinct entities in order to account for various phenomena. For example, a common realist argument, arguably found in Plato, is that universals are required for certain general words to have meaning and for the sentences in which they occur to be true or false. Take the sentence "Djivan Gasparyan is a musician". The realist may claim that this sentence is only meaningful and expresses a truth because there is an individual, Djivan Gasparyan, who possesses a certain quality: musicianship. Thus it is assumed that the property is a universal which is distinct from the particular individual who has the property.

...
Wikipedia