How might synesthesia have influenced Arthur Rimbaud’s “Voyelles”?

In Arthur Rimbaud’s sonnet "Voyelles" ("Vowels"), the poet assigns a specific color to each vowel, a technique that may be linked to the concept of synesthesia—the involuntary association of two different senses, such as sound and sight.12

Rather than necessarily reflecting a personal neurological condition, Rimbaud’s use of synesthesia in "Voyelles" is often interpreted as an application of Charles Baudelaire’s theory of correspondances. This theory posits that sensory experiences are interconnected and that poetry can evoke these links to reveal deeper, hidden realities.13

Rimbaud’s approach was also driven by his desire to become a voyant ("seer") by systematically practicing "le dérèglement de tous les sens" ("the derangement of all the senses"). By intentionally undermining his normal sensory perceptions through various means, he sought to expand his consciousness and access a spiritual "unknown," allowing these visions to dictate the structure and imagery of his poetry. While some suggest the poem was inspired by a child’s colored alphabet book or alchemy, it remains a quintessential example of the Symbolist effort to use sensory associations to communicate ineffable intuitions.413