The unidirectionality of metaphor
An important observation made by conceptual metaphor theorists is that conceptual metaphors are unidirectional. This means that metaphors map structure from a source domain to a target domain but not vice versa. For example, while we conceptualise LOVE in terms of JOURNEYS, we cannot conventionally structure JOURNEYS in terms of LOVE: travellers are not conventionally described as ‘lovers’, or car crashes in terms of ‘heartbreak’, and so on. Hence, the terms ‘target’ and ‘source’ encode the unidirectional nature of the mapping.
Lakoff and Turner (1989) observed that unidirectionality holds even when two different metaphors share the same domains. For example, they identified the two metaphors PEOPLE ARE MACHINES and MACHINES ARE PEOPLE, which are illustrated in examples (17) and (18), respectively.
Although these two metaphors appear to be the mirror image of one another, close inspection reveals that each metaphor involves distinct mappings: in the PEOPLE ARE MACHINES metaphor, the mechanical and functional attributes associated with computers are mapped onto people, such as their speed and efficiency, their part-whole structure and the fact that they break down. In the MACHINES ARE PEOPLE metaphor, it is the notion of desire and volition that is mapped onto the machine. This shows that even when two metaphors share the same two domains, each metaphor is distinct in nature because it relies upon different mappings.
