I listened to Penn on a Youtube video:http://www.youtube.com/watch?v=Q0N6bh_qB58
He tries to explain how someone can be an atheist and an agnostic. This simply isn't true or even possible. He claims that the theist and atheist are beliefs.
Belief should never be used in the same sentence when describing a theist or atheist.
Theist and atheist positions are not beliefs. They are not based on beliefs. In fact, nothing is based on a belief. A belief is no better than an opinion. A belief says I dont know. Belief is not a reason, it is the possible result of some knowledge. Theist and atheist positions are based on knowledge. A belief may or may not result from that knowledge. A person gets their theistic knowledge from the bible or other religious source. Many get their theistic knowledge by just living in a theistic society. You can not go thru life without being exposed to theistic concepts. After he gets the information he may accept it (theist), he may choose to not accept it (atheist) or he may reserve judgment until he acquires more knowledge (agnostic). All three positions are mutually exclusive.
One of the positions is actually true. God either does or does not exist. Calling something that is true a belief is absurd. Truth and belief are mutually exclusive. Not knowing what position is true does not make it less true. The theist doesnt claim he believes in god. The theist claims god exists. So positive are some of these theists that they will fly airplanes into buildings. One does not act this way over a mere belief.
I am atheist. I reject the theist claim. I also reject the belief that someone can be an atheist/agnostic.