It is Written in the Book
All good Catholics know that nominalism is a Bad Thing. Nominalism is the substitution of “names” for universal “natures” as a tool for explaining the world. We need to name or label natural objects, put them into mental filing systems, in order to organize our world into tidy universal categories and patterns—but we have no way of knowing, the nominalist says, what “real” natures underlie those patterns and categories. Maybe there is no universal nature, and the pattern is invented by us for the sake of convenience; or maybe there is a pattern, but it is obscure to human eyes.