Hi Barbara: As teachers in a given course, we are the experts. We have a curriculum and learning outcomes we want to accomplish. More times than not, textbooks will lay out the material in a different order. So, reordering is a common activity. Better authors will compartmentalize their subjects so that a chapter from the middle of the book will stand on it's own. This is especially helpful for courses where students roll in and out at different times. We have to make our resources work for us for maximum benefit. Regards, Barry