The best question to ask yourself when evaluating your use of voice in a paper is, "Does the paper sound like me?"
When your using voice in a paper, it is supposed to reflect you.
Voice adds YOUR style and personality to the paper. It shows your enthusiasm for the subject and engages the reader. The word choice of your paper should reflect the emotions of YOU (the writer), reflect the purpose of the paper, and the understanding of the audience. Your voice/tone should be consistent throughout the paper.
