Maybe we should ask ourselves why it is that ethical relativism seems plausible to many people in spite of that fact.

I think the answer is that many people 'back into' relativism. They are confronted by a range of conflicting moral judgments and principles and there seems to be no way to prove that one and only one judgment or principle is correct.

This gets us into Professor Sidgwick's second question: What are the alternatives to ethical relativism. To avoid being backed into relativism, there must be an alternative.

Science is one alternative, but it seems unable to do the job. There is a long history of doubt concerning the ability of scientific methods to yield values, value judgments, moral principles, and moral ideals.

But if we cannot use science to prove moral principles, then how can we say that one principle is superior or correct?