One particular language mistake that I see occasionally and hear quite often on news shows is the uncertain antecedent. It’s a stylistic error, not a grammar one. Here’s an example:

Bob told Tom that his brother had called him and was drunk. He was very upset.

Whose brother is he referring to, Bob’s or Tom’s, and who is the “he” who was upset? It could be any of the three men referred to, although if it was the drunken brother, the “was” should have been “had been” to stay grammatical. This confuses the reader or listener. It can be clumsy or awkward to keep repeating names in order to avoid this problem, but a skillful writer can find ways to do it. One way is to use “he himself” or “his own.”