Anathem leads you down a garden path: The first few chapters happen in a compound that seems a lot like a monastery here on Earth, except that it’s sort of like a university too. The avout who live inside its walls study philosophy and theoretics, having contact with the outside world for only ten days each year.
“Avout”? Stephenson invents words that straddle the two perspectives, like “concent” (the compound isn’t quite a convent; it studies thought, so let’s bring in some of the word “concentrate’) and “saunt” (revered thinkers aren’t saints, but savants, which kind of works if you remember how Latin U and V are the same letter). Indeed, the book title itself is one of these, a cross of “anthem” and “anathema”. The words soon become familiar, and depending on the context, and maybe your prior knowledge of classical languages and religious rituals, you can figure many of them out, but if you don’t want to, there is a glossary at the end of the book.
It all feels very comfortable and familiar. And then Erasmus, the relater of the story, is pulled from this safe environment and thrust into the outside world, which resembles a version of our own in a slow decline. The world needs the help of Erasmus and others from the concent, and from other similar communities across the planet. This is a global crisis, and it has something to do with something in the sky.
From here, the story snowballs alarmingly in ways that would spoil the surprise for me to even hint at. Every step is plausible, but the plot grows exponentially and the climax is out of this world.
All through the story, the characters engage in Dialog, extended discussions covering seemingly random topics like philosophy, geometry, nuclear physics, the many-worlds hypothesis, and consciousness. These topics are very much not random, though, and they play a pivotal role in the plot.
Stephenson borrows heavily from the classics, deliberately, with reasons that turn out to be sensible in terms of the plot. It’s clear that he’s having fun breaking the fourth wall. If you’re not trained in philosophy you’ll probably fail to link the historical characters mentioned in Anathem with their equivalents in Earth history—I certainly did—but it doesn’t matter a lot. There’s plenty of references you will still get.
I’ve read a few Neal Stephenson books, including his classics Snow Crash and Cryptonomicon. I feel compelled to point out that Stephenson is normally terrible at writing endings, but with Anathem he lands a satisfying denouement.