The selectivity of a medium arises from the way in which it formalizes phenomena within its own constraints. Any medium facilitates, emphasizes, intensifies, amplifies, enhances or extends certain kinds of use or experience whilst inhibiting, restricting or reducing other kinds. There are losses as well as gains. A medium closes some doors as well as opening others, excludes as well as includes, distorts as well as clarifies, conceals as well as reveals, denies as well as affirms, destroys as well as creates. The selectivity of media tends to suggest that some aspects of experience are important or relevant and that others are unimportant or irrelevant.
Mediation is tied to the distribution of power in society.
Selection and exclusion of all kinds favour the realities of some groups rather than others. An awareness of mediation can have a positive function in research and pedagogy. More interestingly, perhaps, we may attempt the difficult task of noticing what is not there. In recent times the phenomenon of absence has been described as 'absent presence' by Jacques Derrida. Just as with any physical tool, both the nature of language and its use involve selectivity.