I am reading the book Faulks on Fiction: A Story of the Novel in 28 Characters by Sebastian Faulks. I will probably have more to say about the contents of this book later, but now I am more interested in the book itself. Published in Great Britain by BBC Books, the volume is a trade paperback of less than 400 pages, yet it seems larger and heavier than most books of this length. Furthermore, the book is something like a bear trap. Open it and it wants to spring shut. To read it requires using both hands to hold it open. After a chapter or two, one's hands might even begin to get tired from the effort.
If Faulks on Fiction is a two-handed book, most of the books I read are one-handed books, mostly trade paperbacks that I can easily hold open with one hand, leaving the other hand free to take notes, drink tea, scratch my nose or whatever.
Then there are no-hands books, those that lie open on any flat surface. I have such a book on my breakfast table now, The Genesis of Science by James Hannam. Not only does the book stay open while I eat, I can leave it open all day without fear it will suddenly spring shut. I chose this as my breakfast book specifically because of this quality. My hands tend to get messy as I eat breakfast.
My wife, who since childhood has had the use of just one hand, always prefers hardbacks to paperbacks because they will stay open more easily.
We have all kinds of ways of categorizing our books. Mostly we sort them by author or subject matter, but some may group them by size or even color. Some keep paperbacks away from hardbacks or old books away from new books. Most of us separate, even if only in our minds, books we've read from those we haven't read, as well as from those we are in the process of reading. Grouping books by how many hands it takes to hold them open is just one more way.