 Ancient inquiries into the nature of social phenomena introduced questions that remain active today: Which features of the world are products of humans or society, and which are products of nature? What does it mean to say that something is a social creation? A central concern of Sophism, a school of Greek philosophy in the fifth century BCE, was the contrast between nature (phusis) and custom, law, habit, or convention (nomos). In particular, they debated the sources of justice, law, and language: are these rooted in phusis or in nomos?