Mathematics
A Gentle Introduction to Bayesian Statistics
Our 10,000th explainer. Prior, likelihood, posterior — the three ideas that quietly reshape how you reason under uncertainty.
Issue No. 312 · The Weekly Foundation
The foundation everything
else is built on.
14,300+ expert-reviewed explainers across science, finance, technology, health, and the humanities — written so the first 20% of any field is faster to learn, easier to remember, and free of jargon.
Free. No paywalls. 14,300+ expert-reviewed explainers, last reviewed within 18 months.
From the Editors
Today’s Reading
Three explainers, hand-picked by the editorial desk. Each reviewed by three subject-matter experts and stamped with a “Last Reviewed” date.
Economics
Compound Interest, Properly Understood
The single concept behind retirement accounts, sovereign debt, and the long arc of markets — explained without the fintech gloss.
Biology
How the Immune System Recognizes You
Self versus non-self, innate and adaptive layers, and the elegant molecular logic that keeps the body from attacking itself.
The Index
The 62-Domain Index
14,300+ expert-reviewed explainers, organized by field. Every entry written to our in-house Clarity Standard and updated on an 18-month review cycle.
A flagship format
Core Knowledge Paths: the first 20% of any field, sequenced.
Each path is a curated sequence of 8 to 14 explainers that builds one field from the ground up — the foundational concepts every expert relies on, in the order they make sense. No videos, no quizzes, no certificates. Just the reading.
Readers complete Core Knowledge Paths in 47% less time than comparable MOOCs, according to a 2023 internal study of 2,140 learners.
Paths are sequenced, not curated playlists. The first explainer assumes nothing; each subsequent one builds on the last. When you finish, you have the foundational vocabulary, the core mental models, and the small set of canonical examples that the rest of the field is written in.
- Foundations of Economics — 12 explainers · ~3 hrs
- How the Mind Works — 10 explainers · ~2.5 hrs
- Programming from First Principles — 14 explainers · ~4 hrs
- The Structure of Modern Physics — 11 explainers · ~3 hrs
Read it. Listen to it. Read it in your language.
The same explainer, three formats.
Foundational knowledge should not be locked behind a screen or a single language. Every article is available as clean plain-text, as human-narrated audio, and in translation.
Audio: 38 narrated courses.
Long-form explainers voiced by narrators chosen for clarity, not performance. Listen on a walk, on a commute, or while cooking dinner.
Translation: now in 9 languages.
Our translation initiative launched in 2024. Spanish, Mandarin, and Arabic lead the catalogue, with Portuguese, French, German, Hindi, Japanese, and Russian close behind.
