The view in conceptual metaphor theory that conceptual metaphors serve to map structure from a source domain to a target domain but not vice versa. For example, while love is conceptualised 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 there is a general constraint on the cross-domain mappings that underpin conceptual metaphor which holds that the mappings are unidirectional.