This paper inquires the ways in which paper folding constitutes a mathematical practice and may prompt a mathematical culture. To do this, we first present and investigate the common mathematical activities shared by this culture, i.e. we present mathematical paper folding as a material reasoning practice. We show that the patterns of mathematical activity observed in mathematical paper folding are, at least since the end of the nineteenth century, sufficiently stable to be considered as a practice. Moreover, we will argue (...) that this practice is material. The permitted inferential actions when reasoning by folding are controlled by the physical realities of paper-like material, whilst claims to generality of some reasoning operations are supported by arguments from other mathematical idioms. The controlling structure provided by this material side of the practice is tight enough to allow for non-textual shared standards of argument and wide enough to provide sufficiently many problems for a practice to form. The upshot is that mathematical paper folding is a non-propositional and non-diagrammatic reasoning practice that adds to our understanding of the multi-faceted nature of the epistemic force of mathematical proof. We then draw on what we have learned from our contemplations about paper folding to highlight some lessons about what a study of mathematical cultures entails. (shrink)

Deictic (or pointing) gestures are traditionally known to have a simple function: to supply something as the referent of a demonstrative linguistic expression. I argue that deixis can have a more complex function. A deictic gesture can be used to _say something_ in conversation and can thereby become a full discourse move in its own right. To capture this phenomenon, which I call _rich demonstration_, I present an update semantics on which deictic gestures can indicate situations from a conversation’s context (...) and those situations coherently connect to prior discourse to generate information. (shrink)