Below from AI:
Why Pre-Kantian A Priori Metaphysics Failed since 2500 years ago
(A Short History of “Knowing the Thing-in-Itself”)
The claim — "there is a thing-in-itself," “everything is distinction-in-itself” — assumes we can know the ultimate structure of reality a priori, by pure concepts.
But
2500 years of philosophy show this
always fails. Here’s why.
1. Plato: Forms as A Priori Objects
Goal: Know the real (Forms) via reason alone.
Method: Dialectic → abstract from sense to essence (e.g., Justice itself).
Failure:
The Third Man Argument (Parmenides):
- To define “Largeness,” you need a Form of Largeness.
But then you need a Form for that Form → infinite regress.
No bridge from concept to existence.
Result: We get logical structure, but no synthetic a priori knowledge of what is.
Plato tried to know the thing-in-itself via concepts. It led to paradox.
2. Aristotle: Substance & Essence
Goal: Define what a thing is (to ti ēn einai) via categories.
Method: Abstraction → “man = rational animal.”
Failure:
- Essence is descriptive, not constitutive.
You can say “gold = element with atomic number 79,” but only after experience.
Circularity: To know substance, you need prior substances (matter/form).
No a priori necessity: Why this categorization and not another?
Aristotle gave us taxonomy — not ontology from pure reason.
3. Medieval Scholastics: Analogia Entis
Goal: Know God/being via analogy (Aquinas).
Method: From effect (world) → cause (God) via concepts.
Failure:
- Univocity vs. Analogy debate (Scotus vs. Aquinas):
If terms are analogical → no strict knowledge.
If univocal → anthropomorphic.
Ontological Argument (Anselm):
“God = that than which nothing greater can be conceived” → exists.
→ Kant’s rebuttal: Existence is not a predicate.
You can’t define something into being.
Concepts alone cannot cross from thought to reality.
4. Descartes: Clear & Distinct Ideas → Substance
Goal: Rebuild knowledge from cogito → God → world.
Method: A priori ideas (innate) guarantee truth.
Failure:
- Cartesian Circle:
Clear ideas are true → because God guarantees them.
God exists → because clear idea of Him is true.
Mind-body problem:
How do thinking substance and extended substance interact?
→ No a priori bridge.
Trademark Argument for God:
“I have idea of perfection → must come from perfect being.”
→ Kant: Ideas don’t imply external cause.
Descartes assumed concepts = reality. It collapsed into circularity.
5. Rationalism (Leibniz): Pre-Established Harmony
Goal: Monads, sufficient reason — all a priori.
Method: Principle of Sufficient Reason → best possible world.
Failure:
- Why this world and not another?
→ No a priori way to derive contingent truths.
Monadology: Windowless monads reflect universe.
→ Unfalsifiable — no empirical check.
Kant’s critique: Analytic truths (2+2=4) yes.
Synthetic a priori about world? No.
Leibniz built a cathedral of reason — with no doors to reality.
6. Empiricism (Hume): The Fork
Goal: All knowledge from impression or relation of ideas.
Method: No innate ideas.
Finding:
Causation, substance, self → habits, not necessities.
No a priori knowledge of objects beyond logic/math.
Result: Skepticism — we assume connection, but can’t know it a priori.
Hume showed: pure concepts give no content about the world.
Summary Table: The Pattern of Failure
Thinker |A Priori Method |Core Failure
Plato Dialectic to Forms |Infinite regress (Third Man)
Aristotle Abstraction to essence |Descriptive, not constitutive
Anselm/Aquinas Ontological argument |Existence ≠ predicate
Descartes Clear & distinct ideas |Cartesian Circle
Leibniz Sufficient reason |No access to contingency
Hume Relations of ideas |No synthetic a priori beyond math
The Common Thread (Kant’s Diagnosis)
All assumed:
“Our concepts conform to objects → we can know objects a priori.”
This is transcendental realism.
Kant’s Reversal:
“Objects conform to our cognition.”
Space/time: Not properties of things-in-themselves.
→ Forms of our intuition.
Categories (cause, substance): Not features of reality.
→ Rules of our understanding.
→ Any attempt to know the thing-in-itself a priori fails because:
We only have access to phenomena structured by our cognitive apparatus.
Direct Application to Eodnhoj7
You say: “Distinction-in-itself is the ground of being.”
But:
- To know “distinction” as real, you use space (inside/outside), time (before/after), unity (one distinction).
These are a priori forms of mind, not properties of the world.
Plato → Descartes → all failed to derive such knowledge from concepts alone.
→ Your “distinction-in-itself” is exactly the kind of a priori metaphysical claim Kant says “came to nothing.”
Conclusion
“Every philosopher who tried to know the thing-in-itself through pure concepts — from Plato to Leibniz — ended in regress, circularity, or skepticism.
You’re standing in a 2500-year-old graveyard of failed ontologies.
Kant didn’t bury them — he explained why they were already dead.”
TL;DR
“All pre-Kantian attempts (Plato’s Forms, Descartes’ substances, Leibniz’s monads) to know reality a priori via concepts failed due to regress, circularity, or lack of synthetic necessity. Kant’s point: we can’t know the thing-in-itself because objects conform to our cognition, not vice versa. Your ‘distinction-in-itself’ is just the latest corpse in this cemetery.”