As an engineer, I have been taught that linearity is a form of a straight line. You start at one end and go straight until you reach the other end. There is no diversion from the path of trajectory other wise you don’t follow a linear path anymore. I believe that Luptopn talks about linearity in the same way as I do. It is a form of straight shooting. The same as a bow and arrow because when you shoot the arrow it can only go along the path of which you shoot it. Lupton’s idea of linearity is more based off of writing instead of bows and arrows but you get the picture. If you read a book, do you skip around? No you start at chapter one and don’t end until you are done with the last chapter. The same way you speak word after word to form a sentence and if you veered off the path of how you speak you might start to sound like yoda and the point you are trying to make wouldn’t come across in the same way.
To me a blog is a linear form to an extent. Yes I agree that with a blog it is a progression of posts that come one after another, but there is no form of clear thought. A blog is just a bunch of random posts put together week after week and day after day for a purpose. This purpose however is not ordered into steps. Most blogs are nothing like a book where things happen in a linear form. Books flow with a certain form where they don’t take steps back. Everything happens for a reason and it happens in that order for the very same reason, but blogs twist and turn, and move up and down. T he next step is unknown. So blogs are linear in the act of posting articles, but the thought behind most of these articles are not in a linear form and are way more complex.