Poetry is a form of literature that uses aesthetic and rhythmic qualities of language-such as phonaesthetics, sound symbolism, and metre-to evoke meanings in addition to, or in place of, the prosaic ostensible meaning. Poetry has a long history, dating back to the Sumerian Epic of Gilgamesh. Early poems evolved from folk songs such as the Chinese Shijing, or from a need to retell oral epics, as with the Sanskrit Vedas, Zoroastrian Gathas, and the Homeric epics, the Iliad and the Odyssey. Poetry uses forms and conventions to suggest differential interpretation to words, or to evoke emotive responses. Devices such as assonance, alliteration, onomatopoeia and rhythm are sometimes used to achieve musical or incantatory effects. The use of ambiguity, symbolism, irony and other stylistic elements of poetic diction often leaves a poem open to multiple interpretations. Similarly figures of speech such as metaphor, simile and metonymy create a resonance between otherwise disparate images-a layering of meanings, forming connections previously not perceived. This book outlines the literary devices used in poetry.