Conceptual metaphor theory, developed by Lakoff and Johnson, argues that metaphor is not merely a literary decoration but a fundamental cognitive mechanism by which we understand abstract domains in terms of concrete ones. Systematic mappings like ARGUMENT IS WAR ("She attacked my position," "He shot down my idea") and TIME IS MONEY ("spending time," "investing hours") structure everyday thought and language across cultures. Metonymy, by contrast, involves a within-domain mapping where one entity stands for a related entity — "The White House announced" (building for institution), "I'm reading Shakespeare" (author for works). Both metaphor and metonymy generate novel extensions productively: once a conceptual metaphor is established, speakers can create new expressions that follow the mapping without having encountered them before.
Collect ten everyday expressions about a single abstract concept (time, love, ideas) and identify the underlying conceptual metaphor — notice how consistent the source domain is across expressions. Distinguish metaphor from metonymy by testing whether the mapping crosses domains (metaphor) or stays within one (metonymy). Analyze how the same concept is metaphorically structured differently across languages to see which mappings are universal and which are culturally specific.
Most people learn about metaphor as a literary device — Shakespeare comparing a beloved to a summer's day, poets finding fresh images for old emotions. Linguists George Lakoff and Mark Johnson challenged this picture in their 1980 book *Metaphors We Live By*, arguing that metaphor is not decoration but cognition: the primary mechanism by which humans understand abstract domains in terms of concrete ones. The metaphors are not in the poems; they are in the mind, and language reflects them.
A conceptual metaphor is a systematic mapping between a source domain (typically concrete, embodied, and well-understood) and a target domain (typically abstract). The mapping is structural: it transfers relational properties from source to target. ARGUMENT IS WAR, for instance, maps positions, attacks, defenses, strategies, and victories from warfare onto argumentation. This is why we say "She demolished his argument," "He defended his position," "I won that debate," and dozens of similar expressions — all drawing on the same underlying mapping. The metaphor is systematic and productive: once established, speakers can generate novel extensions (like "outflank the counterargument") that follow the same structure without having encountered them before.
Metonymy works differently. Instead of a cross-domain structural mapping, it involves substitution within a domain based on contiguity: one entity stands for a related entity in the same conceptual space. "The White House announced" (institution for the people inside it), "I'm reading Woolf" (author for works), "We need more boots on the ground" (clothing for soldiers) — each involves a systematic contiguity relation. Metonymy is not sloppy or loose reference; it follows constrained, conventional relations (part-for-whole, container-for-contents, producer-for-product) that speakers and hearers recognize as coherent.
From your prerequisite study of lexical semantics, you know that word meanings are organized in networks: synonymy, antonymy, hyponymy, polysemy. Conceptual metaphor adds another dimension — much of the lexicon's organization for abstract vocabulary is built through metaphorical extension from concrete meanings. Look at academic vocabulary: "comprehend" (to grasp), "conceive" (to take in), "theory" (Greek: a seeing). These are frozen metaphors, once vivid, now conventionalized. The mental lexicon does not store abstract meanings in isolation; it anchors them to concrete domains through the same cross-domain mappings that produce living metaphors.
The key diagnostic for distinguishing metaphor from metonymy is the domain test: does the mapping cross conceptual domains, or does it stay within one? "The pen is mightier than the sword" maps writing onto warfare — different domains, so it is metaphor. "She's been reading Austen all week" substitutes one concept (author) for another in the same domain (the author's works) — same domain, contiguity relation, so it is metonymy. Some complex cases involve both, but the domain test handles the core cases and gives you a principled basis for analysis rather than an intuitive guess.