 Natural science is a branch of science concerned with the description, prediction and understanding of natural phenomena, based on empirical evidence from observation and experimentation. Mechanisms such as peer review and repeatability of findings are used to try to ensure the validity of scientific advances. Natural science can be divided into two main branches, life science or biological science and physical science. Physical science is subdivided into branches, including physics, chemistry, astronomy and earth science. These branches of natural science may be further divided into more specialized branches also known as fields. In Western society's analytic tradition, the empirical sciences and especially natural sciences use tools from formal sciences, such as mathematics and logic, converting information about nature into measurements which can be explained as clear statements of the laws of nature. The social sciences also use such methods, but rely more on qualitative research, so that they are sometimes called soft science whereas natural sciences, insofar as they emphasize quantifiable data produced, tested and confirmed through the scientific method, are sometimes called hard science. Modern natural science succeeded more classical approaches to natural philosophy, usually traced to ancient Greece. Galileo, Descartes, Bacon and Newton debated the benefits of using approaches which were more mathematical and more experimental in a methodical way. Still, philosophical perspectives, conjectures and presuppositions, often overlooked, remained necessary in natural science. Scientific data collection, including discovery science, succeeded natural history, which emerged in the 16th century by describing and classifying plants, animals, minerals, and so on. Today, natural history suggests observational descriptions aimed at popular audiences.