In TST, every idea falls under one of three broad categories: empirical, rational, or irrational.
In 30 Philosophers, I defined the empirical side more specifically by dividing empirical ideas into two subtypes: sensory and nonsensory. Sensory ideas are things we directly perceive, like a tree, a bike, or the color red. Nonsensory ideas are still empirical, but they require tools or indirect detection, things like microorganisms, distant galaxies, radio waves, or ultraviolet light. More interesting still, that distinction can vary by species and even by individual. What is sensory to a hammerhead shark may be nonsensory to a human, and what is sensory to a sighted person may be nonsensory to someone who is blind.
That three-part split matters. It gives us a simple way to sort thoughts by how they relate to reality and evidence. But within each of those categories, there is still room for further classification. Here, I want to do for irrational ideas what I already did for empirical ones: define their subtypes more clearly. We can handle the subtypes of rational ideas later.
Not all irrational ideas are equally bad.
Irrational Ideas: The Subtypes
Some irrational ideas are merely speculative. They are not yet supported well enough to count as rational or empirical, but they could still turn out to be true. Others are disproven. Those are ideas for which the evidence currently runs strongly against them.
That distinction matters.
A speculative idea is still alive. A disproven idea, as currently stated, is not. That does not mean it could never be revised, refined, or reshaped into something more defensible. It just means that in its present form, the evidence has gone against it.
That is an important difference.
Speculative versus Disproven
A lot of new ideas begin as speculative. That is not an insult. It is just their category.
Before an idea is well supported, it lives in the speculative zone. It may be promising. It may even be brilliant. But until it gains enough support, it remains irrational in the technical sense of my framework. It has not yet earned rational or empirical standing.
Einstein’s theory of relativity is a good example. At first, it was speculative. Then the evidence began to accumulate. Eventually, it earned enough support to move into the category of empirical truth.
That is how progress often works.
Ideas begin as possibilities. Some mature into stronger ideas. Others collapse under evidence.
History as a Rational Category
History is an interesting case because it usually belongs under rational ideas.
Historical claims relate indirectly to the material world. They are about what happened, not what is happening right now in front of us. We reconstruct the past from evidence, inference, and the simplest explanation that best fits what we know.
That makes historical knowledge rational in this framework. It is grounded in evidence, but usually through indirect reconstruction rather than direct present observation.
And importantly, historical ideas can be disproven by evidence.
Suppose someone says Homo sapiens painted a particular cave in Spain. But the evidence we currently have points to Neanderthals being there during that period, and not Homo sapiens. In that case, the simpler and better-supported conclusion is that the cave paintings belong to Neanderthals, not Homo sapiens.
Now, someone could still say, “I think it is possible Homo sapiens were there too.” That would not yet be a rational historical conclusion. It would be a speculative idea. It could still, in theory, turn out to be true if new evidence emerged. But until then, it remains speculative.
That is the key.
When we talk about fiction, deep history, or ideas about the unknown, whether currently unknown or perhaps unknowable, those ideas often fall under the irrational category in a logical setting. Not because they are worthless, but because they have not yet earned enough support to rise higher.
Why Use the Word Irrational?
I realize the word irrational can sound harsher than intended.
It can sound like I mean foolish, absurd, or obviously wrong. But that is not quite what I mean. I chose the term mainly because it pairs cleanly with rational.
Empirical ideas are grounded in observation.
Rational ideas are grounded in thought about observation.
Irrational ideas are the ideas that do not yet have enough support, or that have lost that support.
That is the structure.
So yes, irrational includes bad ideas, but it also includes new ideas, untested ideas, imaginative ideas, and speculative ideas. Some of those may eventually prove useful. Some will not.
Astrology as a Disproven Idea
Astrology is a good example of a disproven idea.
Astrology makes claims about human personality, behavior, and life patterns based on the positions of physical objects like the planets and the sun. It is often elaborate. It can look systematic. It can even appear internally consistent in parts.
But internal consistency is not enough.
An idea can be logically tidy and still fail when tested against reality. When that happens, I would not usually say it is “rationally consistent but wrong.” I would say it is logically or internally consistent, but its empirical predictions do not pan out.
That is a cleaner way to say it.
And in the case of astrology, the forms of it that exist today, at least the ones I am aware of, have repeatedly failed empirical testing. That places them in the disproven category.
So while astrology may still function as mythology, symbolism, or entertainment for some, it does not currently stand as a rational or empirical truth claim.
The Apathy and Exploration of Speculation
William James surfaces only narrowly in my work, but where he does, he matters. In 30 Philosophers, I frame Pragmatism as the view that practical impact can matter more than intellectual accuracy, and I quote James’s famous line that the pragmatic method asks what practical difference it would make if one idea rather than another were true. In that sense, James gives voice to a very human impulse: if an idea helps us live, decide, or move forward, we tend to give it room, even before it is fully settled.
In TST, that impulse does not become permission to believe whatever feels useful. Instead, it shows up more narrowly under the explorative agnostic within irrational ideas. That is where speculation lives when it has not yet earned rational or empirical standing, but has also not been disproven. The explorative agnostic is willing to look, listen, compare, and even lightly model possibilities, while still withholding belief. That is the key guardrail. Curiosity is allowed. Commitment is not. That keeps exploration from sliding into dogma.
This is where the split between explorative agnosticism and apathetic agnosticism becomes useful. An explorative agnostic says, “That idea is speculative, so I will stay agnostic, but I am interested enough to follow it.” An apathetic agnostic says, “That idea is speculative, so I will stay agnostic, and I do not care enough to spend time on it.” Both positions withhold belief. Both avoid pretending speculation is knowledge. The difference is interest.
You can apply that response to each speculative idea one at a time, and also to speculation as a whole. Maybe you enjoy dabbling in ideas about extraterrestrial life, consciousness, simulation theory, mystical claims, or the edges of physics. Fine. Be explorative if you want. But use a framework. Stay agnostic. Keep the idea in the speculative category until it earns more. That way you can explore without becoming the intellectual version of a crazy cat person, surrounded by fascinating possibilities you mistakenly started treating as facts.
That, to me, is the healthy use of speculation. If a claim is disproven, avoid it. If it is speculative, decide your level of interest. Then choose between apathetic agnosticism and explorative agnosticism. Apathetic means you do not care to pursue it. Explorative means you do. Either way, the discipline is the same: enjoy the wondering, but do not let wonder outrun evidence. The agnostic in both cases still says, “Let me know if new evidence shows up.”
Conclusion: A Better Way to Think About Irrational Ideas
The main point here is simple.
“Irrational” is not just a trash bin for nonsense. It is a wider category that includes both speculative and disproven ideas.
That gives us a better framework.
It lets us say:
some ideas are not yet supported, but still possible;
some ideas are currently contradicted by evidence;
and some ideas may move from one category to another over time as new evidence arrives.
That movement is part of how knowledge grows.
So in TST, irrational ideas are not all the same. Some are early-stage possibilities. Some are dead ends. Knowing the difference helps us think more clearly, speak more precisely, and avoid confusing imagination with knowledge.