I'm interested in hearing the answer to this, as well. Good question.
Since we're on the subject....(how does an atheist differentiate between right and wrong?)
http://asktheatheist.com/?p=776
If it harms neither you nor anybody else then it must be right, if it does the opposite then it has to be wrong.
Regarding morality:
1. Empathy and Consideration of Effect: Humans have the ability to comprehend another's experience, feelings, etc. Using this ability one can consider whether one's actions will be "correct" or "good" by the person(s) affected by such action. Such consideration of effect prior to action is part of any rational direction of one's actions.
2. Utilitarianism: "All action should be directed toward achieving the greatest happiness for the greatest number of people."
3. Naturalistic: "…any animal whatever, endowed with well-marked social instincts, the parental and filial affections being here included, would inevitably acquire a moral sense or conscience, as soon as its intellectual powers had become as well, or nearly as well developed, as in man. . . . " –
Charles Darwin.
4. Social Contract: We agree to standards of conduct, the "rules of society" in order to gain the advantages of society. Which is similar to Utilitarianism.
5. Chaos Theory and Consideration of Effect: I find that the implications of Chaos theory as it applies to morality are profound. Consider what is commonly known as "The Butterfly Effect", that is the fact that in a Complex Dynamic System small changes in input can cause profound changes. The basic implication is that any action taken may have drastic consequences. Responsibility, even if only to oneself, therefore demand that consideration as to the impact of one's actions be given.
I think that Einstein stated it fairly well, "A man's ethical behaviour should be based effectually on sympathy, education, and social ties; no religious basis is necessary. Man would indeed be in a poor way if he had to be restrained by fear of punishment and hope of reward after death."
