Christian: Why do you believe that God does not exist?
Atheist: Simple, there is no evidence for existence of God.
Christian: How is no evidence for existence of God, evidence for nonexistence of God?
Atheist: What do you mean by that?
Christian: Well, if CSI or FBI find no evidence that Kray Brothers murdered Bill Bob, does that mean Kray Brothers did not murdered Bill Bob?
Atheist: No, but no one can know for sure if they did or did not murdered Bill Bob.
Christian: You are correct, that position is called agnosticism. Simply means no enough knowledge to decide.
Atheist: So for me to be an atheist, I need to have evidences that God does not exit?
Christian: Yeap. Moreover even if one succeed in refuting all arguments for existence of God, that by itself does not entail nonexistence of God.
Atheist: How about the problem of Evil?
Christian: Well, we already answered that one last week.
Atheist: Yeah right! How about evolution?
Christian: Even if evolution is true, it does not entail nonexistence of God, because God could create a universe that evolves.
Atheist: That is possible! Well give me time to think about that, and I will come with arguments against existence of God.
Christian: I am looking forward. Thank you for a wonderful chat.
Atheist: Thanks back to you.