Refer to the original authors by their full names the first time you talk about them. If the author has a title (Dr., Professor, President etc.), use it. Never misspell an author's name. After you have given the author's full name, you may then shorten it to using the last name only. There are occasional exceptions. It is okay to refer to Shakespeare as Shakespeare - you don't ever have to call him William Shakespeare because it is clear and apparent who he is. Other "superstar" authors may also be referred to this way. Unless, however, your author is a generally accepted cultural icon, use his or her full name. How do you know if he or she is? If you used their last name alone - would everyone know whom you were speaking about? Really? NEVER refer to your author by his or her first name only. (However close you may feel to him or her because of his/her writing... he/she is NOT your friend!!) Just remember to be respectful and to give the authors their due, and you won't go wrong.