A Brief Description of Realism and Nominalism

In my writings, and especially in the paper titled "Getting Realistic about Nominalism," I mention realism and nominalism. Each of the terms "realism" and "nominalism" has more than one meaning in philosophy. Here I will explain, very briefly, the meanings most relevant to that paper.

The most traditional forms of realism and nominalism are realism and nominalism with respect to universals. Universals are items, like properties and relations, that can belong to (or be exemplified by) more than one object. For example, the color green is a universal, because more than one object can be green. For another example, the relation of being north of is a universal, because more than one pair of objects on Earth can stand in this relation (with one object north of the other).  

Realism with regard to universals is the doctrine that universals are real items; they really have being of some kind. This means that the real world is not just a collection of concrete things, like tables and chairs. Instead, the real world contains universals (properties, relations, etc.) along with the concrete things. 

Nominalism, on the other hand, states that our talk about universals is only figurative. For example, a nominalist would claim that when we say "red is a color," we are not really referring to an item named "red" that has many instances or examples. Instead, the statement that "red is a color" must be understood in some other way, as a sort of figure of speech.

Besides realism with regard to universals, there also is a realism with regard to abstract entities. This doctrine states that abstract entities (for example, mathematical entities) are real items. Nominalism with regard to abstract entities states that talk about abstract entities is only figurative.

This explanation of realism and nominalism has been very brief; it does not capture all the fine points. To get a more complete picture, please consult an encyclopedia of philosophy or an introductory book covering this topic. One starting point would be the Armstrong or Russell references in "Getting Realistic about Nominalism."