Heuristics for choosing/writing good textbooks (see also here):
- Has exercises
- Exercises are interspersed in the text, not in large chunks (better at the end of sections, not just at the end of chapters).
- Solutions are available but difficult to access (in a separate book, or on the web), this reduces the urge to look the solution up if one is stuck.
- Of varying difficulty (I like the approach Concrete Mathematics takes: everything from trivial applications to research questions).
- I like it when difficulty is indicated, but it's also okay when it's said clearly in the beginning that exercises are not marked for difficulty (making them mystery boxes).
- Takes many angles
- Has figures and illustrations. I don't think I've encountered a textbook with too many yet. (See Visual Complex Analysis for an example of doing this well.)
- Has many examples. I'm not sure yet about the advantage of recurring examples. Same point about amount as with figures.
- Includes code, if possible. It's cool if you tell me the equations for computing the likelihood ratio of a hypothesis & dataset, but it's even cooler if you give me some sample code I can use and extend along with it.
- Uses typography
- You can use boldface and italics and underlining for reading comprehension, example here.
- Use section headings and paragraphs liberally.
- Artificial Intelligence: A Modern Approach has one- to three-word side-notes describing the content of each paragraph. This is very good.
- Distinguish definitions, proofs, examples, case-studies, code, formulas &c.
- Dependencies
- Define terms before they are used. (This is not a joke. Population Genetics uses the term "substitution" on p. 32 without defining it, and exercise 12-1 from Naive Set Theory depends on the axiom of regularity, but the book doesn't define it.)
- If the book has pre-requisites beyond what a high-schooler knows, a good textbook lists those pre-requisites and textbooks that teach them.
- Indicators
- Multiple editions are an indicator for quality.
- Ditto for multiple authors.
- A conversational and whimsy style can be nice, but shouldn't be overdone.
- Hot take: I get very little value from proofs in math textbooks, and consider them usually unnecessary (unless they teach a new proof method). I like the Infinite Napkin for its approach.
- Wishlist
- Flashcard sets that come together with textbooks. Please.
- 3blue1brown style videos that accompany the book. From Zero to Geo is a great step in that direction.
I agree. Maybe it's time to repost The Best Textbooks on Every Subject again? Many of the topics I want to self-study I haven't found recommendations for in that thread. Or maybe we should create a public database of textbook recommendations instead of maintaining an old forum post.