The prosthetic extends the effective reach of an object beyond what it is normally capable of reaching. But, in creating a relation between the object of interest and the initial object, the prosthetic drops away, or withdraws. So, for example, when I need to reach a box at the top shelf I might extend my rather puny reach with the help of a broom handle. The broom handle becomes a prosthetic, which means that it also drops away as I achieve my goal of reaching the box. This type of extension is closely tied to Marshall McLuhan’s argument that media extends us:
All media are extensions of some human faculty – psychic or physical. The wheel is an extension of the foot, the book is an extension of the eye, clothing an extension of the skin, [and] electric circuitry an extension of the central nervous system. Media, by altering the environment, evoke in us unique rations of sense perceptions. The extension of any one sense alters the way we think and act – when these ratios change, men change. (26-41)But we need to extend McLuhan’s definition beyond the human to state that all objects extend other objects. Cables extend information, aglets extend the life of shoelaces, and remote controls extend the couch. Each prosthetic either withdraws or forces other objects to withdraw in its use.