A scientist is a person who researches to advance knowledge in an area of the natural sciences. By modern definitions, many scientists are required to have advanced degrees in an area of science and careers in various sectors of the economy such as academia, industry, government, and nonprofits pertaining to their discipline. In classical antiquity, there was no real ancient analog of a modern scientist. Instead, philosophers engaged in the philosophical study of nature called natural philosophy, a precursor of natural science. Though Thales (circa 624–545 BC) was arguably the first scientist for describing how cosmic events may be seen as natural, not necessarily caused by gods, it was not until the 19th century that the term scientist came into regular use after it was coined by the theologian, philosopher, and historian of science William Whewell in 1833. History The roles of "scientists", and their predecessors before the emergence of modern scientific disciplines, have evolved considerably over time. Scientists of different eras (and before them, natural philosophers, mathematicians, natural historians, natural theologians, engineers, and others who contributed to the development of science) have had widely different places in society, and the social norms, ethical values, and epistemic virtues associated with scientists—and expected of them—have changed over time as well. Accordingly, many different historical figures can be identified as early scientists, depending on which characteristics of modern science are taken to be essential. Some historians point to the Scientific Revolution that began in 16th century as the period when science in a recognizably modern form developed. It wasn't until the 19th century that sufficient socioeconomic changes had occurred for scientists to emerge as a major profession. Classical antiquity Knowledge about nature in classical antiquity was pursued by many kinds of scholars. Greek contributions to science—including works of geometry and mathematical astronomy, early accounts of biological processes and catalogs of plants and animals, and theories of knowledge and learning—were produced by philosophers and physicians, as well as practitioners of various trades. These roles, and their associations with scientific knowledge, spread with the Roman Empire and, with the spread of Christianity, became closely linked to religious institutions in most of European countries. Astrology and astronomy became an important area of knowledge, and the role of astronomer/astrologer developed with the support of political and religious patronage. By the time of the medieval university system, knowledge was divided into the trivium—philosophy, including natural philosophy—and the