Have you ever stumbled upon a reference to a blog called “Astral Codex Ten” or its predecessor, “Slate Star Codex,” in an online discussion? You see people talking about it with a kind of reverence, mentioning incredibly long essays on everything from psychiatry and AI to medieval history and book reviews. You try to find a simple explanation, but you just get lost in a rabbit hole of even more complex ideas. If that sounds familiar, you are in the right place.
I remember the first time I clicked on a link to an Astral Codex Ten post. The article was about 8,000 words long, which is roughly the length of three university essays. My initial reaction was, “Who has the time for this?” But I started reading, and before I knew it, I was completely absorbed. The writer, Scott Alexander, has a unique talent for taking a complicated, often dry subject and making it feel like a fascinating detective story. This blog is not just a website; it’s a gateway to a unique way of thinking.
So, let’s demystify it. What exactly is Astral Codex Ten?
From Slate Star Codex to Astral Codex Ten: A Blog’s Journey
To understand Astral Codex Ten, often abbreviated as ACX, you need to know a little about its past life. Before ACX, there was “Slate Star Codex” (SSC). For years, SSC was the home of Scott Alexander’s writing, and it built a massive following among intellectuals, tech workers, scientists, and philosophers. It was the central hub of the “rationalist” community, a group we will talk about more later.
The blog was thriving, but in 2020, it ran into a problem that many internet writers fear. A reporter from the New York Times was writing a story about the blog and intended to use Scott Alexander’s real name (Scott Siskind) in the article. Now, for most writers, this would be a dream. But Scott, who is a psychiatrist, had always written under a pseudonym. He was worried that patients searching for him online would find his controversial political and philosophical essays instead of information about his medical practice. He felt this could damage the trust essential for therapy.
In protest, he made the difficult decision to delete the entire Slate Star Codex blog. The internet rationalist community was sent into a frenzy. It was a dramatic moment that highlighted the tensions between modern journalism, online anonymity, and free speech.
After a short period of silence, Scott Alexander returned. He started a new blog on the publishing platform Substack, which offered better tools for writers to control their content and audience. He named this new blog “Astral Codex Ten.” If you say “Slate Star Codex” quickly, it sounds a bit like “Astral Codex.” It was a clever, anagram-like nod to his old home, signaling that the spirit of the blog lived on, even if the name and address had changed.
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Who is Scott Alexander? The Mind Behind the Blog
So, who is the person behind these legendary essays? Scott Alexander (his pen name) is a psychiatrist and writer based in the San Francisco Bay Area. Knowing his profession is key to understanding his work. His medical and psychological training shines through in almost everything he writes. He approaches topics with a clinician’s eye for detail, a scientist’s respect for data, and a deep empathy for the human condition.
He is not a journalist trying to get clicks, nor is he an academic writing only for other experts. He is a curious individual working through ideas in public. He will often start an essay with a question he genuinely wants to answer, like “How well do antidepressants actually work?” or “Why did some ancient civilizations collapse?” He then spends thousands of words meticulously examining studies, considering counterarguments, and building a case. His writing style is humble, self-deprecating, and incredibly thorough. He is quick to point out when he might be wrong, which is a refreshing change from the confident certainty you often find online.
In my opinion, this humility is what makes his writing so powerful. He is not trying to win an argument; he is trying to find the truth. He models a kind of intellectual honesty that is desperately needed today. When you read his work, you are not just learning facts; you are learning how to think.
What Kind of Topics Does Astral Codex Ten Cover?
The range of topics on ACX is astonishingly broad. It can feel random at first, but a common thread runs through it all: a commitment to clear thinking, reason, and evidence. Here are some of the main categories you will encounter.
Deep Dives into Science and Medicine
Given his background, some of Scott’s most impactful writing is in this area. He has written extensively about psychiatric medications, the replication crisis in psychology, and the intricacies of medical research. For example, he might take a new, hyped-up scientific study and spend hours dissecting its methodology, pointing out potential flaws that the mainstream media coverage missed. He makes complex statistical concepts understandable for the layperson. If you are interested in health, science, or how to interpret the news about the latest “breakthrough,” these posts are invaluable.
Philosophy, Politics, and Society
This is where the blog can get controversial. Scott explores ideas from moral philosophy, political tribalism, social justice, and forecasting the future. He is politically heterodox, meaning he doesn’t cleanly fit into standard left-right boxes. He might write a post sympathetic to some social justice ideas and then another post critiquing others. This frustrates people who prefer simple narratives, but it delights those who enjoy nuanced, non-ideological analysis.
A famous example from the SSC days was his long essay “I Can Tolerate Anything Except The Outgroup.” It is a deep exploration of tribal psychology and why we are often kinder to people within our group and harsher to those outside it. Essays like this try to explain the underlying mechanics of our social and political world, rather than just taking sides.
Unforgettable Book Reviews
Scott Alexander’s book reviews are legendary. They are not simple summaries or critiques. They are often massive essays that use the book as a starting point for a wide-ranging exploration of the book’s core theme. A review of a book about a historical event might turn into a full-blown analysis of that era, complete with graphs, data from other sources, and philosophical musings. People often joke that you do not need to read the book itself after reading his review, because he has synthesized and expanded upon it so thoroughly. These reviews are a fantastic way to discover new books and ideas you would never have encountered otherwise.
More Than a Blog: The ACX Community and The Rationalist Movement
Astral Codex Ten is not just a one-way broadcast from Scott to his readers. A huge part of its appeal is the community that has grown around it. This community is part of the broader “rationalist” movement, which is centered on ideas from the blog “LessWrong.” The core goal of rationalism is to improve human reasoning and overcome cognitive biases—the common thinking errors we all make.
The ACX comment section is famously high-quality. Readers include professors, programmers, researchers, and experts of all kinds. They add new data, point out errors, and continue the discussion in incredibly insightful ways. Often, the comments are as enlightening as the post itself. Scott also runs a popular “Advertise on ACX” program where people can pay a small fee to post ads for their projects, startups, or personal quests, leading to a wonderfully eclectic mix of content.
Furthermore, the community actively participates in things like the “ACX book review contest” and “Prediction Tournaments,” where people compete to make the most accurate forecasts about future events. This creates a living, breathing ecosystem of people who are genuinely trying to understand the world better.
How to Start Reading Astral Codex Ten (Without Getting Overwhelmed)
Facing a blog with hundreds of massive essays can be intimidating. Here is my personal advice on how to get started without feeling lost.
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Start with the “Greatest Hits”: Look for curated lists of the best posts. You can find these by searching for “best of slate star codex” or “best of astral codex ten.” This will lead you to the most beloved and accessible essays.
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Follow Your Interests: Browse the archives by category. If you are interested in medicine, start there. If you love history, find his history-related posts. You do not have to read everything in order.
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Read the Comments (Selectively): After you read a post, skim the comments. You do not need to read all 500 of them, but look for the top-voted ones. They often contain crucial updates, corrections, or brilliant insights that build on the article.
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Take Your Time: Do not try to rush. These are not quick blog posts; they are more like mini-books. It is okay to read one essay over a few days. The goal is understanding, not speed.
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Subscribe: Consider subscribing to the free newsletter on Substack. This delivers new posts directly to your email, so you can keep up with new content at your own pace.
Conclusion
Astral Codex Ten is a unique and valuable corner of the internet. It is a blog run by a thoughtful psychiatrist who explores science, philosophy, and culture with an unparalleled depth and intellectual honesty. It is more than just a collection of essays; it is the heart of a community dedicated to reasoning well and seeking the truth, even when it is uncomfortable. While it can be dense at first, diving into ACX is a rewarding experience that can fundamentally change how you think about the world. It is a testament to the power of one curious mind sharing its journey with others.
Frequently Asked Questions (FAQ)
Q1: Is Astral Codex Ten free to read?
A: Yes, all main posts on Astral Codex Ten are completely free to read. Scott Alexander offers a paid subscription on Substack, but this is primarily for bonus content like the ACX podcast and the ability to comment. The core essays remain free and accessible to everyone.
Q2: What is the difference between Slate Star Codex and Astral Codex Ten?
A: The main difference is the name and the platform. Slate Star Codex was the original blog, which was deleted in 2020. Astral Codex Ten is its successor on Substack. The writing style, topics, and author are the same. The new name is a playful variation of the old one.
Q3: What are some of the most famous articles to start with?
A: Some classic starting points include:
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“Meditations on Moloch” (a philosophical exploration of destructive competition)
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“I Can Tolerate Anything Except The Outgroup” (on tribal psychology)
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“Book Review: The Precipice” (on existential risks to humanity)
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“Who By Very Slow Decay” (a powerful personal essay about his work as a psychiatrist).
Q4: What is the “rationalist community”?
A: The rationalist community is a loose global movement focused on applying evidence, reason, and cognitive science to improve thinking and decision-making. They are interested in topics like AI safety, effective altruism (using evidence to do the most good), and overcoming cognitive biases.
Q5: Why did Scott Alexander delete Slate Star Codex?
A: He deleted it in protest after a New York Times reporter indicated they would publish his real name in an article. Scott, being a practicing psychiatrist, was concerned about the impact this could have on his relationship with his patients, as his blog contains many controversial opinions.
