The fundamental tenet of Conceptual Metaphor Theory is that metaphor operates at the level of thinking. Metaphors link two conceptual domains, the ‘source’ domain and the ‘target’ domain. The source domain consists of a set of literal entities, attributes, processes and relationships, linked semantically and apparently stored together in the mind. These are expressed in language through related words and expressions, which can be seen as organized in groups resembling those sometimes described as ‘lexical sets’ or ‘lexical fields’ by linguists. The ‘target’ domain tends to be abstract, and takes its structure from the source domain, through the metaphorical link, or ‘conceptual metaphor’. Target domains are therefore believed to have relationships between entities, attributes and processes which mirror those found in the source domain. At the level of language, entities, attributes and processes in the target domain are lexicalized using words and expressions from the source domain. These words and expressions are sometimes called ‘linguistic metaphors’ or ‘metaphorical expressions’ to distinguish them from conceptual metaphors.
For proponents of Conceptual Metaphor Theory, thought has primacy over language. The theory was not intended to account for language in use, which is merely the surface manifestation of more important phenomena. Nonetheless, patterns of word use are the main evidence presented for the theory. These linguistic data have tended to be generated intuitively, either by the researcher or by informants, but in recent years some researchers are beginning to analyze naturally occurring language data.
Proponents of Conceptual Metaphor Theory argue that few or even no abstract notions can be talked about without metaphor: there is no direct way of perceiving them and we can only understand them through the filter of directly experienced, concrete notions. The conceptual metaphor a purposeful life is a journey is cited widely in the literature. This is realized linguistically through expressions such as “He got a head start in life. He’s without direction in life. I’m where I want to be in life…”. It is difficult to find linguistic expressions about the development of an individual’s life which are not also used to talk about literal journeys. Other metaphors are used to talk about different aspects of life; Lakoff cites a purposeful life is a business. It is very difficult to find expressions used to talk about the subject of life which are not metaphorical in some way. If it is true that abstract subjects are generally talked about using metaphor, and a mass of linguistic evidence has been gathered to support this contention, a close examination of the metaphors used can be an important key to the way people have mentally constructed abstract domains.
Conceptual metaphor theorists claim that all metaphors both hide and highlight aspects of the target domain. For instance, the conceptual metaphor understanding is seizing, discussed by Lakoff and Turner suggests that an idea is a concrete object which can be metaphorically grasped and then held. This highlights a familiar aspect of understanding new ideas but hides the important point that sometimes understanding comes slowly, with some effort, and that ideas are reinterpreted by each individual.
The poetic metaphors that had been analyzed in research in literature and philosophy for many years were of minor importance for conceptual metaphor theorists. If conceptual metaphors help people to understand abstract subjects of such central importance as life and communication, then the metaphorical expressions that should form the focus of study are the conventional, frequent ones. These will provide clues to the conceptual structures that both reflect and shape the thought patterns of the community. To describe these, a common technique is to identify the linguistic metaphors used to talk about a topic, and from these postulate underlying conceptual metaphors which are presumed to motivate them. The researcher can then consider which aspects of the target domain are highlighted and hidden by the metaphor.
In many cases, linguistic metaphors represent subconscious choices on the part of the speaker or writer, whose choice of language is partly constrained by the conceptual structures shared by members of his or her community. Metaphors can also help people to talk about difficult, emotionally intense or uncommon experiences, and thus, according to conceptual metaphor theory, to think about them. Gwyn analyzed the metaphors that seriously ill people used to talk about their experience, and drew conclusions about their thoughts and feelings on the basis of these.