Why were Sophists among the first thinkers to demand reasons for moral claims?

The Sophists were among the first thinkers to demand that moral claims be justified by reasons because they cultivated the art of defending or attacking a thesis through rigorous argumentation.1

By observing that different nations held conflicting rules of conduct regarding sacred matters—such as marriage and burial—the Sophists concluded that many moral codes were based on convention rather than absolute truth. This skepticism toward traditional morality led them to explore alternative approaches and necessitated the use of reason to evaluate or defend these claims.23

While their focus on debating skills was sometimes criticized as eristic—or argument for the sake of victory—their emphasis on the importance of language and the definition of ethical terms was instrumental in bringing argumentation to a central position in Greek thought. By challenging pupils to provide accounts for their beliefs, the Sophists helped establish the practice of subjecting moral claims to critical inquiry, a method that later influenced Socrates and the development of Western ethics.14