Arguments Aren't Necessarily Linear

Conceptually speaking, however, an argument is not a serial affair. It is sequential, I grant you, because some statements have to follow others, but this doesn't imply that its nature is neccesarily serial. We usually string Statement B after Statement A, with Statements C, D, E, F and so on following in that order--this is serial structuring of our symbols. Perhaps each statement logically followed from all those which preceded it on the serial list, and if so, then the conceptual structuring would also be serial in nature, and it would be nicely matched for us by the symbol structuring.

But a more typical case might find A to be an independent statement, B dependent upon A, C and D independent, E depending on D and B, E dependent upon C, and F dependent upon A, D, and E. See, sequential but not serial? A conceptual network but not a conceptual chain. the old paper and pencil methods of manipulating symbols just weren't very adaptable to making and using symbol structures to match the ways we make and use conceptual structures.

Douglas Engelbart, Douglas Engelbart, Augmenting Human Intellect (October 1962)