African-American writers introduced new themes into American literature dating back to America's inception as colonies of England. Take, for example, Oluadah Equiano--he brought the issue of slavery and its atrocities to the forefront. Also consider Langston Hughes, Countee Cullen and Claude McKay--all poets of the Harlem Renaissance--all wrote about the oppression of African-Americans and their struggle for equality and civil rights. More contemporary authors, such as Maya Angelou and Toni Morrison, all deal with themes of overcoming poverty, hardship and discrimination.  As far as modes of language, many of these writers used colloquial language (everyday language) in their writing, which gives their work an authentic feel, sound and rhythm, allowing readers to experience life exactly as it is.

Um, yes? I think the question you may be asking here is which African-American authors have contributed the aforementioned themes, issues and modes, so here's my abbreviated "top 5" list:

1. Alice Walker -- Her novel "The Color Purple" used both colloquy and other devices to best demonstrate the trials and triumphs of the African-American life.

2. Robert Hayden -- This relatively unpublicized poet of the Harlem Renaissance is best known for his work "Those Winter Sundays." The poem is comparable to Roethke's "My Papa's Waltz," as it deals with the relationship between father and son.

3. Langston Hughes -- He'll probably make everybody's list due to his significance, but no list of great authors would be complete without him. Whether we're talking about "The Weary Blues," "Harlem," or any one of his other pieces, Hughes sets the bar for fellow writers.

4. Maya Angelou -- Her books and poems made her the poet laureate, among other things. She also read at Clinton's inauguration, but turned down an invitation to do so at our current president's.

5. Toni Morrison -- "I Know Why the Caged Bird Sings." Enough said, right there. This novel by itself would put Morrison on the list, but her other works simply supplement her reputation.

Hope this little guide helps out a bit.

Have African American writers introduced new themes and language into American literature?

Certainly all of the works of the Harlem Renaissance are critically important, but one work that isn't mentioned above in Richard Wright's Native Son. Not only was this the first novel by an African-American to be selected as a book-of-the-month selection, but it forced the ideas of racial inequalities and social justice for African Americans into the mainstream consciousness of our country. Although chillingly violent, the philosophical elements of Bigger Thomas's attempts to establish his own identity amid the chaos of a hostile white world resonates as strongly today as in did when first published in 1940.

I do believe that this is valid.  I would suggest that like all great authors, African- American writers have helped to enhance the discourse with integrating new and different ways of viewing the world.  Thinkers like Langston Hughes wrote about a voice of dissent in a world and time period of pure assent.  The idea of being able to experience a new way of viewing the world that might have been apart from the mainstream has now become almost commonplace, but African- American writers like DuBois or Hughes or Hansberry or Morrison were instrumental in this process.  Without them, it is difficult to conceive the presence of multiple narratives that is such an integral part to our learning environment today.