Invariance
As a result of the emergence of these ideas, a preoccupation for conceptual metaphor theorists in the late 1980s and early 1990s centred on how metaphoric mappings could be constrained (Brugman 1990; Lakoff 1990, 1993; Lakoff and Turner 1989; Turner 1990, 1991). After all, if metaphor is ultimately based on image schemas, with chains of inheritance relations giving rise to highly abstract and specific metaphors like LOVE IS A JOURNEY, ARGUMENT IS WAR and so on, it is important to establish what licenses the selection of particular image schemas by particular target domains and why unattested mappings are not licensed.
There appear to be certain restrictions in terms of which source domains can serve particular target domains, as well as constraints on metaphorical entailments that can apply to particular target domains. For example, Lakoff and Turner (1989) observed that the concept of DEATH is personified in a number of ways (which means that a concept has human-like properties attributed to it, such as intentionality and volition). However, the human-like qualities that can be associated with DEATH are restricted: DEATH can ‘devour’, ‘destroy’ or ‘reap’, but as Lakoff (1993: 233) observes, ‘death is not metaphorized in terms of teaching, or filling the bathtub, or sitting on the sofa.’ In order to account for these restrictions, Lakoff posited the Invariance Principle:
Metaphorical mappings preserve the cognitive topology (that is, the image schema structure) of the source domain, in a way consistent with the inherent structure of the target domain. (Lakoff 1993: 215)
There are a number of specific death personification metaphors, including DEATH IS A DEVOURER, DEATH IS A REAPER and DEATH IS A DESTROYER, which inherit structures from a more schematic metaphor, which Lakoff and Turner (1989) call a generic-level metaphor: EVENTS ARE ACTIONS (or INANIMATE PHENOMENAAREHUMANAGENTS). What the invariance principle does is guar antee that image-schematic organisation is invariant across metaphoric map pings. This means that the structure of the source domain must be preserved by the mapping in a way consistent with the target domain. This constrains potentially incompatible mappings.
Let’s elaborate this idea in relation to the DEATH metaphors mentioned above. While DEATH can be structured in terms of the kinds of agents we have noted (DEVOURER, REAPER or DESTROYER),it cannot be structured in terms of any kind of agent at random. For example, it would not be appropriate to describe DEATH as KNITTER, TEACHER or BABYSITTER. Agents that devour, reap or destroy bring about a sudden change in the physical state of an entity. This corresponds exactly to the nature of the concept DEATH, whose ‘cognitive topology’ or ‘inherent’ conceptual structure is preserved by the attested mappings like DEATH IS A DESTROYER but not the unattested mapping *DEATH IS A KNITTER.
The Invariance Principle also predicts that metaphoric entailments that are incompatible with the target domain will fail to map. Consider the examples in (23), which relate to the metaphor CAUSATION IS TRANSFER (OF AN OBJECT):
While the source domain for both of these examples is TRANSFER, the first example relates to a STATE and the second to an EVENT. The source domain TRANSFER entails that the recipient is in possession of the transferred entity. However, while this entailment is in keeping with STATES because they are temporally unbounded, the same entailment is incompatible with EVENTS because they are temporally bounded and cannot therefore ‘stretch’ across time. This is illustrated by (24).
The process that prevents entailments from projecting to the target domain is called target domain override (Lakoff 1993).
