So, the book tells us that there exists 4 levels of reading – Elementary, Inspectional, Analytic, and Synoptical --, each building on each other. Think of a tower. Here’s an explanation:

1. Elementary: reading in it’s most basic terms. If you can read this, you are on this level. If you don’t master this level, when for example you read something in a language you can’t understand, you won’t be able to read a book systematically
2. Inspectional: it’s skimming the book to understand what the book is about, how it’s organized. Here your focus is on the form and purpose of a book. Think how you can instantly know if you are reading a recipe vs a manual, even though both are “instructional”. Not because of the content, but because of the title, the headings, etc. In short, it’s doing the best reading possible in a limited amount of time.
3. Analytical: it’s actually reading the book well. How do you build a good mental model to understand the content of the book?
4. Synoptical: it’s making a synthesis of the content of several books with your own judgement and previous knowledge. As an analogy, it’s like each book became a paragraph in an article. You are the author here.

The book is not a philosophical work. It’s very practical. Each one of those levels has its own practical concrete techniques on how to perform them well.

Also, it has tips on specific types of books like math ones, novels, philosophical works etc.

I liked this book because it helped me see texts differently. Like, for example, think about why authors do not give you an outline of their arguments. Why is prose so important even in technical works? Why did Lenin have to spend so much time talking about other people’s ideas and why was that so important?

I think it’s a good book. Adler 100% was not a Communist (he spends a lot of the chapter on Elementary Reading talking about the US in positive terms. I skipped it) but I think his advice was very dialectical in my opinion.

I hope this helps. Did I understand your question?