Metaphor is best conceived not as a textual feature, but as a product of readers responding to texts. In technical discourse, metaphors help readers perform certain physical and mental operations. The technical metaphor can be classified by how it specifically helps readers perform these tasks, that is, by its purpose and method. The technical metaphor can 1) name parts, stressing space; 2) denote actions, stressing time; 3) denote qualities, stressing neither time nor space; or 4) create models, stressing both time and space.