1. Views about right and wrong forms of conduct vary significantly from society to society. (In our own day, we might compare the way in which assisted suicide is condoned in some countries, but not in others).

2. What is right for one individual may not be right for another. (E.g. it might be right for me to have access to your student records, but wrong for someone who is not an adviser to try to do so).

3. Some matters regarded as morally right (or wrong) may at some later date be thought wrong (or right). Consider how attitudes have changed about slavery, or birth control over the course of several centuries.

If we add some form of linking premiss such as (4) below, then these considerations would yield a valid argument.

4. If (1), (2), and (3), then there are no generally valid moral principles.

Therefore 5. There are no generally valid moral principles--which is the thesis of Moral Relativism.

But is the argument sound? Is each of its premisses true? We might compare fashions in clothes--they vary across societies, among different individuals, and over time. And there does appear to be no generally valid principles that govern fashions--each of us is free to dress pretty much as we like.

But consider a different kind of case: the principles of a proper diet (or another one: the principles of grammar in natural languages). Diets differ across societies, among individuals, and over time. But, here, we do want to say there are some basic principles that govern diet--there some basic needs that every diet needs to fulfill. So (4), as a universal generalization appears to be false--some variation is compatible with the presence of a set of basic principles. But is morality more like fashion, or like diet (or the rules of grammar)? The task then becomes to determine whether there are any generally accepted moral principles--e.g. that inflicting un-necessary suffering is wrong--which are accepted even though many other matters are the subject of conflicting opinions? (The debate over assisted suicide, for example, appears to turn in large part on the factual question of whether the practice will spread to non-terminal cases of illness). And are all moral disputes over moral principles (as opposed to factual questions)? We will return to the topic of Moral Relativism when we read Plato’s Meno.

1. Acting ‘morally’ (i.e. acting in accordance with established moral principles) requires, on at least some occasions, restraining ourselves from pursuing our own interests out of regard or respect for the rights or interests of others. (Morality, in short, has a social dimension to it.)

2. Acting morally requires, on at least some occasions, that act in a way that does not promote our own personal advantage.

3. Freed of all external constraints human beings will always pursue their own personal advantage. (Known as the Thesis of Psychological Egoism)

4. Freed of all external constraints human beings will choose not to act in accordance with the dictates of morality.

5. All those who choose to act in accordance with the dictates of morality do so only because of the presence of external constraints.

Most philosophers would accept the truth of (1) and (2), but reject (3)--the thesis of Psychological Egoism. However, when Plato addresses this topic he appears to accept (1) and (3), but not (2). The Republic contains an extended defense of the thesis that ‘acting justly’ is always in our best interests--always to our advantage, even if we must sometimes restrain ourselves out or regard or respect for the rights or interests of others.

But the philosophies of Moral Relativism and Moral Cynicism have gained many, many supporters since the sophists first expressed them in 5th-century Athens.