Yes, empirical and rational categories of the Idea of Ideas applies to all words. Not absolute, but in their use.
Empirical words observe. Rational words organize.
A word is empirical when it directly describes the material world. A word is rational when it helps the mind structure, compare, group, relate, or organize what is being described. And finally, a word functions irrationally when it points to something asserted as real, but not supported by evidence, reason, or coherent grounding.
Words like cat, tree, roof, smoke, and red are empirical when they point directly to things or properties in the material world. Words like number, category, cause, system, equality, justice, schema, and theory are rational because they describe reality indirectly. They help the mind organize experience.
Some rational words are conceptual, such as number, cause, category, justice, and theory. Others are structural, such as is, are, of, on, if, then, and because. These words do not usually describe material things directly. Instead, they are rational and help connect ideas. For example, “are” binds a subject to an action, identity, category, or state.
This is why an empirical sentence can still use rational words. “Three cats are playing on a tin roof” is an empirical sentence because it directly describes material things and actions: cats, playing, and a tin roof. “Infinite cats are playing on a tin roof” is irrational.
Some words also shift categories depending on use. Root is empirical when it names the root of a tree, but rational when it names the root of a number. Field is empirical when it names a meadow, but rational when it names a magnetic field or a field of study.
