I don’t want to be dogmatic about the details, though: my basic point is that I find it helpful, when considering what books to keep, to have explicit criteria! Some of my criteria are: useful reference book, likely to reread, part of a collection that is important to me, hard to replace, I really will get around to reading this soon honest really I will. I don’t care about the specifics of your criteria: the importance is having the criteria, not what they are. Then go through your books, and mentally label each one that you want to keep with one of those criteria. If you’re not sure you want to keep it, that’s okay; just take your best guess as to a label and keep it for now. I suspect that doing that once will allow you to get rid of a fair number books, and that doing it again a year later will also be allow you to get rid books that were on the borderline the first time.

For buying books, though, I will be dogmatic. Treat all the books you own now as sunk costs: don’t worry about getting around to reading them. Sign up for Amazon Prime. And stop buying books that you think you might read. Instead, every time you start reading a book, decide right then what book you’ll read once you’re done with your current book; if necessary, order it with Amazon Prime, knowing that you’ll receive it within two days. (Alternatively, wander over to your favorite bookstore after dinner, or go to the library, or something: Amazon Prime is useful as a safety valve, since you know any book is never more than two days away, but there’s no particular reason to use it at all exclusively.) And then read that book next!

Based on your description, you’ll save the cost of Amazon Prime within a couple of months, setting aside all storage issues. Or maybe not – I seem to recall that you still buy a fair number of used books. In that case, the calculus gets a bit harder: you can impose a rule of “no more than 3 recently purchased unread books”, or something. The point is to avoid speculative buying: don’t buy a book unless you know when you are going to read it. If you can’t answer that question, then you aren’t getting any benefit from buying it now: you’ll be able to get your hands on the book when/if you eventually feel an urge to read it.

As for my own situation: we have more books than space, and our solution is that about 80% of the books we own are packed in boxes in our storage space, not to be opened until we buy a house. And I’ve found that it’s been only about three times in two years that I really wished I could look at something that was in those boxes. According to your system, does that mean all these books, or at least all the replaceable ones, are discards?

As for buying new books, I have this problem: I’d say I read about a third of the books that I buy. But I’d also say that if I had to predict, at point of purchase, which ones I’d read, I would do a very bad job. I suppose I could start actually recording these predictions and seeing whether my intuition on this is right!

The technique is instead very quickly to form a first impression of Keep/Maybe/Delete. If you find yourself hesitating, it’s a Maybe, so move on. The idea is to get through a large volume of books instead of agonizing over each small decision. I’ve found that I could get through a very large number of books fairly quickly, and I had put a surprising number into the delete category. I used this technique cleaning out the books from my parents’ house. I think I must have gone through 20 or so boxes and I got rid of perhaps a third of them. Of course, this was fairly easy, since my parents accumulated a lot of books in which I had little interest.

I used this technique with books some time ago, and unsurprisingly, I chose to delete many fewer of them — perhaps only 5%. I’ll have to reread your post and then make another pass. If I get rid of another 5-10% that would be a big step forward for me.

My wife is a lot better than me about using the library. I did update my library card recently — after about 15 years! — and I checked out a few books. Having a deadline is a great impetus for reading them. After I finished them they went back to the library and didn’t clutter up my place. It was great!

Having a “book budget” is a good idea. I should think about that some more.