30 Philosophers, Chapter 18, Peter Abelard, Touchstone 47: The Idea of Ideas.

The Idea of Ideas is a new look at epistemology. It is a secular epistemology: a reality-guided system for classifying ideas as empirical, rational, or irrational. Furthermore, truth is calibrated to alignment with reality. All ideas including words, phrases, statements, and questions are more true the more they align with reality. 

The Idea of Ideas asserts empirical, rational, and irrational entities exist in the Material World, independent of the minds of beings who can discover, label, and use them as ideas. When this theory refers to “beings,” it’s referring to any entity with advanced cognitive abilities or with the capacity for abstract thinking, whether here on Earth or not, as well as certain advanced AI systems. In this framework, the terms “ideas” and “mental constructs” are interchangeable. Both serve as the cognitive tools that beings use to make sense of the Material World. Both are mental models used to build representations and understanding whether empirical, rational, or speculative.

It implies many metaphysical things that help bridge science, philosophy, and fiction. Ideas represent entities like physical matter and energy, things on Earth like dirt, the color red, gravity, and even things we detect with tools like radio waves. Ideas can be rational like logic, justice, and beauty, or irrational like Valhalla, or a fictional realm like the Forbidden Forest in Harry Potter. The best part is that this framework allows you to easily determine if something is empirically true, rationally true, or falls into the irrational category.