This is my first post on verb tenses which comprise another problematic area in the English language. This post is specifically on what I call the "double past." This question is an example: "What did she said?"
The question above commits the error of the double past because it uses both did and said. The reason for the mix-up is the seeming simplicity of the past tense rule: if it happened in the past, use the past tense. However, in this case, there are two verbs (did and said). It's seems natural to use the past tense for both because whatever happened did happen in the past.
The thing is, for a case like this, the verb is do (did) and say (said) is not a verb. Instead, say is a noun, a name for whatever the "she" in the sentence wanted to communicate.
No one likes someone with a double life. English doesn't like this case of the double past either. Have a nice evening!