So a textbook is useful to the extent that it helps its reader pass a class or a test. Whereas a (non-fiction) book is useful to the extent that its author manages to convey his or her reasons for setting out to write the book in the first place; for conveying what they found interesting or remarkable, not (as determined by the bevy of textbook publishers) what's gonna be on a test. I agree. I think that I took a slightly incredulous tack earlier because I imagine a chemistry, or even a psychology, textbook to be prima facie and less controversially useful, more than a textbook on history could be, although it is history that this entire post is concerned with. Thank you for the insight. And like I said, I am an abiding fan of non-fiction. Already on page 87 of Destiny Disrupted.