Which school of thought argues that universal concepts are mere words without substantial reality?

Nominalism is a philosophical school of thought that asserts that universal concepts, such as "beauty" or "justice," do not have an independent or substantial existence outside of the names or labels we use to describe them. According to nominalists, these concepts are simply linguistic constructs that do not correspond to any real, universal essence shared among particular instances. For instance, when we refer to "cats," nominalism holds that we are discussing mere categories or groupings made by humans, rather than invoking a real, shared quality that exists independently of the individual cats themselves.

This perspective contrasts significantly with realism, which posits that universal concepts do indeed have a real and substantial existence beyond mere words, suggesting they reflect fundamental truths about the world. Rationalism and empiricism address the nature of knowledge and belief rather than the existence of universals, focusing instead on reason and sensory experience, respectively. Thus, nominalism uniquely emphasizes the idea that universals are not more than arbitrary terms we use to organize our understanding of reality.