Welcome to The Nonlinear Library, where we use Text-to-Speech software to convert the best writing from the Rationalist and EA communities into audio. This is: A short conceptual explainer of Immanuel Kant's Critique of Pure Reason, published by jessicata on June 3, 2022 on LessWrong.
Introduction
While writing another document, I noticed I kept referring to Kantian concepts. Since most people haven't read Kant, that would lead to interpretation problems by default. I'm not satisfied with any summary out there for the purpose of explaining Kantian concepts as I understand them. This isn't summarizing the work as a whole given I'm focusing on the parts that I actually understood and continue to find useful.
I will refer to computer science and statistical concepts, such as Bayesianism, Solomonoff induction, and AI algorithms. Different explainers are, of course, appropriate to different audiences.
Last year I had planned on writing a longer explainer (perhaps chapter-by-chapter), however that became exhausting due to the length of the text. So I'll instead focus on what still stuck after a year, that I keep wanting to refer to. This is mostly concepts from the first third of the work.
This document is structured similar to a glossary, explaining concepts and how they fit together.
Kant himself notes that the Critique of Pure Reason is written in a dry and scholastic style, with few concrete examples, and therefore "could never be made suitable for popular use". Perhaps this explainer will help.
Metaphysics
We are compelled to reason about questions we cannot answer, like whether the universe is finite or infinite, or whether god(s) exist. There is an "arena of endless contests" between different unprovable assumptions, called Metaphysics.
Metaphysics, once the "queen of all the sciences", has become unfashionable due to lack of substantial progress.
Metaphysics may be categorized as dogmatic, skeptical, or critical:
Dogmatic metaphysics makes and uses unprovable assumptions about the nature of reality.
Skeptical metaphysics rejects all unprovable assumptions, in the process ceasing to know much at all.
Critical metaphysics is what Kant seeks to do: find the boundaries of what reason can and cannot know.
Kant is trying to be comprehensive, so that "there cannot be a single metaphysical problem that has not been solved here, or at least to the solution of which the key has not been provided." A bold claim. But, this project doesn't require extending knowledge past the limits of possible experience, just taking an "inventory of all we possess through pure reason, ordered systematically".
The Copernican revolution in philosophy
Kant compares himself to Copernicus; the Critique of Pure Reason is commonly referred to as a Copernican revolution in philosophy. Instead of conforming our intuition to objects, we note that objects as we experience them must conform to our intuition (e.g. objects appear in the intuition of space). This is sort of a reverse Copernican revolution; Copernicus zooms out even further from "the world (Earth)" to "the sun", while Kant zooms in from "the world" to "our perspective(s)".
Phenomena and noumena
Phenomena are things as they appear to us, noumena are things as they are in themselves (or "things in themselves"); rational cognition can only know things about phenomena, not noumena. "Noumenon" is essentially a limiting negative concept, constituting any remaining reality other than what could potentially appear to us.
Kant writes: "this conception [of the noumenon] is necessary to restrain sensuous intuition within the bounds of phenomena, and thus to limit the objective validity of sensuous cognition; for things in themselves, which lie beyond its province, are called noumena for the very purpose of indicating that this cognition does not extend its application to all that the understanding thinks. But, after all, the possibility of such noumena is quite incomprehensible, and beyond the sphere of pheno...