This is about epistemology — how we humans describe reality using words.

In 30 Philosophers, I explore the evolution of this idea — from the unknowable Dao, to Hume’s logic, to Kant’s filtered reality, and beyond.

In Chapter 18, I introduce the Idea of Ideas — because that’s the point in the evolution where we needed a common set of words to explain the rest of the story.

It’s a modern update of Kant’s core insight:

That human experience shapes what we know.

And that not all ideas are created equal.

Kant drew a line between the world we experience and the world we can’t.

But he didn’t yet have falsifiability — Popper’s principle that a claim must be testable to count as knowledge.

My framework picks up there.

• Empirical ideas describe reality directly — confirmed by observation or measurement.

• Rational ideas describe reality indirectly — they’re logical, structured, and testable. They’re not guesses. They’re true ideas that just happen to be framed in terms of patterns, principles, or math.

• Irrational ideas do neither — they’re untested, untestable, or disproven. That includes astrology, flat Earth, and speculative stories like the many-worlds interpretation of quantum mechanics.

To illustrate, take algebra. It’s a rational tool — but statements using it fall into all three categories:

• “2 + 2 = 4” — That’s empirical, when used to count apples. It directly describes a real-world observation.

• “x² + y² = r²” — That’s rational, describing the logic of a circle in space — abstract, structured, and testable.

• “x + x = 5 when x = 2” — That’s irrational, a disproven claim. It’s mathematically false.

So — is the split in the Idea of Ideas the same as Kant’s?

Yes, essentially. Kant gave us the filter. The Idea of Ideas gives us the labels.