The Meissner effect causes a magnet to levitate above a high-temperature superconductor. Science (from the Latin scientia, 'knowledge'), in the broadest sense, refers to any systematic knowledge or practice. In a more restricted sense, science refers to a system of acquiring knowledge based on the scientific method, as well as to the organized body of knowledge gained through such research.[1][2] This article focuses on the more restricted use of the word. Fields of science are commonly classified along two major lines: Natural sciences, which study natural phenomena (including biological life), and Social sciences, which study human behavior and societies. These groupings are empirical sciences, which means the knowledge must be based on observable phenomena and capable of being experimented for its validity by other researchers working under the same conditions.[2] Mathematics, which is sometimes classified within a third group of science called formal science, has both similarities and differences with the natural and social sciences.[2] It is similar to empirical sciences in that it involves an objective, careful and systematic study of an area of knowledge; it is different because of its method of verifying its knowledge, using a priori rather than empirical methods.[2] Formal science, which also includes statistics and logic, is vital to the empirical sciences. Major advances in formal science have often led to major advances in the physical and biological sciences. The formal sciences are essential in the formation of hypotheses, theories, and laws,[2] both in discovering and describing how things work (natural sciences) and how people think and act (social sciences). Science as discussed in this article is sometimes termed experimental science to differentiate it from applied science, which is the application of scientific research to specific human needs, though the two are often interconnected.