If you analyse anything that you do as a process, then you can quickly establish/see whether it is linear. A lot of what we do can thus be seen to be linear process flow, and even that explosive/connected "discovery" process would be linear if it was broken down (decomposed) into small enough discrete steps. The thing about using the hardcopy reference texts (hardcopy media) though is that it seems non-linear, because it is "fast" (speedy).
It is fast because you can use your trained reading faculties and that media, jumping your attention across a wider span and then focussing in as necessary, in such a way as to minimise the duration of the discrete sequential linear process steps and of any delay intervals between them. You thus accelerate the process.
I think part of that might be a little more complex than it appears on surface study. When I was in college I had the good fortune to take a course taught by Bernard Lonergan that examined the concept of insight and what it represented in terms of human learning and understanding. It was an absolutely mind-bending course.
I won't even attempt to begin to summarize all that we covered in that class. (Those interested in learning more can look here
, or here
.) But one of the topics that was studied at some length was the process of insight and how it was not linear
in that whatever happened at the point of insight (the "aha!" moment) effectively modified our minds (neural patterns) such that although we could not point to a linear progression towards
some points of understanding - we could paradoxically reason our way backwards
(i.e. "explain") how we got there.
And there's enough serious studies that have examined that phenomena to seem to indicate that not all
parts of our reasoning and understanding operate in an exclusively linear fashion - even on an extremely granular level. In fact, real breakthrough thinking and realizations appear to occur as a discontinuous function. A quantum leap if you will.
@IainB - I'll leave you to dissect and play with that as you will. I have no stake in the theory either way so I won't be getting into a long discussion or debate over it. I probably spent more intensive and quality thinking time in that course (mainly thinking about 'thinking') than I ever did with anything before or since. Suffice to say the experience was life changing.