I'm citing an article that appeared in the Washington Post but was authored by a writer (Tom Seppy) for the Associated Press. Do I need to
Since this article has a named author, Tom Seppy, you don't need to mention the Associated Press. You would only have to mention the AP if there was no author given. So in this case, just treat it as a normal newspaper article. The exact format will depend on which citation style you're using (APA, NLM, AMA, etc.) If you have any further questions, please let us know.