 One of the points at which philosophical difficulties arise is in characterizing the sharedness of the attention that is implicated in this developmental trajectory. Christopher Peacocke has argued that the way in which joint attention episodes are shared involves a kind of reciprocal recognition of the other’s recognition of one’s own attention, and that it therefore involves a kind of mutual openness that is analogous to the openness of ‘common knowledge’, as that notion figures in philosophical analyses of communication and convention (see the entry on  convention).  Since joint attention is achieved by young children, its achievement cannot plausibly be thought to make any sophisticated intellectual demands. Peacocke therefore argues that awareness of reciprocated openness must be more fundamental than the intellectual achievement of common knowledge.  He suggests that it should instead be understood as a variety of perceptual awareness that makes such common knowledge possible (Peacocke, 2005). John Campbell shares Peacocke’s view of joint attention as being a perceptual phenomenon, as opposed to a phenomenon that is achieved when one’s perception is reflected on in a certain way, but Campbell differs from Peacocke in taking the person with whom attention is shared to be fellow subject of the joint experience, not an object who figures in the content of the experience that each joint-attender individually has (Campbell, 2002, Ch. 8). Campbell’s attempt to shift the explanation of sharedness from the cognitive to the perceptual domain is rejected by Lucas Battich and Bart Geurts (Battich and Guerts, 2020), who suggest that Campbell’s view suffers from problems that originate in his relational conception of perception. They therefore claim that the issues here cast light on the long-running debates between representation-based and relation-based theories of perception (see the entry on  the problem of perception).