We examine metonymy at psycho‐ and neurolinguistic levels, seeking to adjudicate between two possible processing implementations (one‐ vs. two‐mechanism). We compare highly conventionalized systematic metonymy (producer‐for‐product: “All freshmen read O'Connell”) to lesser‐conventionalized circumstantial metonymy (“[a waitress says to another:] ‘Table 2 asked for more coffee.”’). Whereas these two metonymy types differ in terms of contextual demands, they each reveal a similar dependency between the named and intended conceptual entities (e.g., Jackendoff, 1997; Nunberg, 1979, 1995). We reason that if each metonymy yields a distinct processing time course and substantially non‐overlapping preferential localization pattern, it would not only support a two‐mechanism view (one lexical, one pragmatic) but would suggest that conventionalization acts as a linguistic categorizer. By contrast, a similar behavior in time course and localization would support a one‐mechanism view and the inference that conventionalization acts instead as a modulator of contextual felicitousness, and that differences in interpretation introduced by conventionalization are of degree, not of kind. Results from three paradigms: self‐paced reading (SPR), event‐related potentials (ERP), and functional magnetic resonance imaging (fMRI), reveal the following: no main effect by condition (metonymy vs. matched literal control) for either metonymy type immediately after the metonymy trigger, and a main effect for only the Circumstantial metonymy one word post‐trigger (SPR); a N400 effect across metonymy types and a late positivity for Circumstantial metonymy (ERP); and a highly overlapping activation connecting the left ventrolateral prefrontal cortex and the left dorsolateral prefrontal cortex (fMRI). Altogether, the pattern observed does not reach the threshold required to justify a two‐mechanism system. Instead, the pattern is more naturally (and conservatively) understood as resulting from the implementation of a generalized referential dependency mechanism, modulated by degree of context dependence/conventionalization, thus supporting architectures of language whereby “lexical” and “pragmatic” meaning relations are encoded along a cline of contextual underspecification.