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I want to look at the phrase "without God". My first clarifying question would be "do you mean 'without God's existence' or 'without believing in God'?" The answer to this question will determine how my unasked question about the meaning of "good" will be answered.
If the atheist answers "without God's existence," then it is quite easy. The answer is "yes" and "no"- both meaning the same thing and being just as valid as the other. Since atheists must base their morals on sociocultural contract theory, "good" (which is a moral term) has no objective, intercultural definition. So, one person in one culture may answer the question "yes" (basing his answer on the "goodness" of general behavior), and another person in another culture may answer the question "no" (same basis). If God does not actually exist, this answer does not change even if someone believes that He exists.