Synesthesia in Poetry
In poetry, synesthesia refers specifically to figurative language that includes a mixing of senses. For example, saying "He wore a loud yellow shirt" is an example of synesthesia, as it mixes a visual imagery (yellow) with auditory imagery (loud). Synesthesia is a common poetic technique, but people often do not recognize it as a specific technique.
Synesthesia was popularized by French symbolist poets, such as Charles Baudelaire, Arthur Rimbaud and Paul Verlaine. The symbolists are characterized by their obsession with creating a personal, inner world in their poetry, where things in the outside world act as recurring and personal symbols. Synesthesia was a way to heighten and clarify the symbolic imagery in these poems.
One of the most famous examples of synesthesia in poetry comes from the French poet Arthur Rimbaud, who wrote the poem "Vowels" based on the idea that certain vowels contain certain color associations:
Black A, white E, red I, green U, blue O—vowels, Some day I will open your silent pregnancies: A, black belt, hairy with bursting flies, Bumbling and buzzing over stinking cruelties.
Note here that he gives each vowel a color and also mixes senses in his descriptions: "stinking cruelties" mixes an olfactory sense ("stinking") with a description of an act ("cruelty").
Adding synesthesia to your own poetry can be a useful way to heighten and highlight a specific image or description. In addition, since it is a "mixing" of senses, it can be used to demonstrate confusion or excitement. Synesthesia can add an extra layer of meaning to your poetry and can make imagery more complex and detailed.