This is a book about ethics, about right and wrong and good and bad in human life. But can we really tell moral right from wrong? Morality, many people think, is not like science, which deals in facts, but a matter of values, about which we can only have personal opinions. According to this point of view, there aren't any moral facts, and this explains why people disagree so much over ethical questions. While science is objective, morality is essentially subjective.
This is a very common view of ethics. It is also a very ancient one. Indeed, moral philosophy as an intellectual inquiry may be said to have its origins in a debate about its truth or falsehood. The question of the subjectivity or objectivity of morality provides the focus for the earliest complete works of philosophy - Plato's dialogues. In several of these dialogues, Plato constructs dramatic conversations between his teacher Socrates and various figures well known in ancient Athens. Many of these people were called 'Sophists', a group of thinkers who held that there is a radical difference between the world of facts and the world of values, between physis and nomos to use the Greek words, the difference being that when it comes to matters of value, the concepts of true and false have no meaningful application. By implication, then, in ethics there is no scope for proof and demonstration as there is in science and mathematics; ethical 'argument' is a matter of rhetoric, which is to say, of persuading people to believe what you believe rather than proving to them that the beliefs you hold are true.