Ethics (or moral philosophy) is the study of moral goodness, duties, obligations, values--for example, whether they are absolute or relative--and the reason to be moral at all.

• Ancient Greek Morality: For most Greeks the question "Why be moral?'' is at the heart of morality: one is moral because of the good it yields.  However, Socrates and Plato change the focus of the question to "What is moral?'' and then assume that if we know what is good that will be enough to indicate that we should act morally.

• Thrasymachus: morality is the rules or conventions imposed on others by those in power for their own benefit.  Being immoral is to one's advantage.  That is, being immoral does not necessarily make one unhappy.  Glaucon and Adeimantus: Being moral is beneficial to one; but if one could be immoral without suffering, one would be a fool not to be immoral (Gyges ring).  Even giving the appearance of morality is better than actually acting morally.

• Socrates and Plato: the good consequences of being moral are not what make actions good; rather, actions have good consequences because they are good in themselves (and ought to be done for that reason alone).  Immorality is due to ignorance of the good.
• For Plato, the good is defined in terms of balancing elements of the soul.  As with society, the soul has three parts: the ruling part (rulers are like the soul's reasoning abilities) that knows the truth or essence of what it means to exist in harmony: the virtue of this group is wisdom]. The enforcement part of the soul is our spirit, drive, or commitment; in society this is represented by the "guardians" (police, soldiers) that implement philosophical principles, and their virtue is courage. The productive, get-things-done part of the soul (appetite, lusts, and irrational desires) has its parallel in the workers and artisans in society (whose virtue is moderation.  Justice occurs when the parts of the soul are in harmony, which means that we act in accord with reason, doing what is appropriate given our place in society: this is virtue (aretê).  Human excellence is possible only when justice triumphs and people take one another's interests seriously.  We should therefore be moral because not to do so is to choose not to be harmoniously integrated with oneself.

Objection: if most people in the city are creatures of passion, then the only way they can be controlled is through force.

• Egoism: Every act is motivated by self-interest.

• Plato: no one ever acts knowingly against his/her self-interest.  In this regard, he is like Thrasymachus, except Thrasymachus believed that it is not in one's self-interest to act morally.  For Socrates, this creates an opposition between the interests of the individual and society.  The purpose of Plato's Republic is to show how the two can be reconciled.

• Thomas Hobbes argues that no one ever acts other than to promote his/her own self-interest.  [This rules out the possibility of sacrificing our own interests in the name of the interests of others (altruism).]  If altruism is impossible, then it cannot be a moral duty.
• This last point invokes a particular rule noted by Hume: "ought implies can."  No one can be under a moral obligation to do something which he or she cannot be able to do.  Morality presumes freedom.
Objection: Is there any way to show that Hobbes' egoism (and dismissal of the possibility of altruism) is false?  That is, he does not seem to allow for the possibility of refuting his theory, and in that sense his theory fails Karl Popper's falsifiability criterion of what makes a theory scientific.  A better response on Hobbes' part might be to note how self-interest drives behavior more often than is admitted, and then to give empirical evidence to back that claim up.