Heintz & Scott-Phillips's account of human expression leaves a number of central issues unclear – not least, whether the lack of expression in nonhuman species is attributable to their lack of the relevant metarepresentational abilities, an absence of trust, or a consequence of other factors. In place of their view, we propose a gradualistic account of the origins of human expression.

Comparing knowledge with belief can go wrong in two dimensions: If the authors employ a wider notion of knowledge, then they do not compare like with like because they assume a narrow notion of belief. If they employ only a narrow notion of knowledge, then their claim is not supported by the evidence. Finally, we sketch a superior teleological view.

Gesture and sign form an integrated communication system, as do gesture and speech. Communicative acts in both systems combine categorical linguistic (words or signs) with imagistic (gestures) components. Additionally, both sign and speech can employ modifying components that convey iconic information tied to a linguistic base morpheme. An accurate analysis of communicative acts must take this third category into account.