The book is written in epistolary form. This allows Walker to use Celie's voice. For her, the letters are not just a form of communication (most are not sent) but a safe way of having a voice.
By using this literary style, Walker draws on a long tradition of the epistolary novel in female literature. Black vernacular English is used for Celie’s letters and this fixes the novel within the tradition of African-American writers. Nettie’s letters are written in standard American English and symbolize the colonized tongue. However, as the non-standard dialect is the primary voice it legitimises the dialect and those who speak it.