Roman Jakobson's now classic distinction between metaphor and metonymy defines two primary modes of linguistic thought: on the one hand relations of similarity and dissimilarity, and on the other relations of contiguity or, we might say, dependence and independence. Though they find their most condensed expression in the tropes metaphor and metonymy, these same principles govern phonemic, lexical, and phraseological levels of language, and they operate as well in larger segments of discourse. A piece of fiction or poetry, for example, may develop along lines of association by likeness or through links of sequence and consequence.