science [Lat. scientia =knowledge]. For many the term science refers to the organized body of knowledge concerning the physical world, both animate and inanimate, but a proper definition would also have to include the attitudes and methods through which this body of knowledge is formed; thus, a science is both a particular kind of activity and also the results of that activity. The Scientific Method The scientific method has evolved over many centuries and has now come to be described in terms of a well-recognized and well-defined series of steps. First, information, or data, is gathered by careful observation of the phenomenon being studied. On the basis of that information a preliminary generalization, or hypothesis, is formed, usually by inductive reasoning, and this in turn leads by deductive logic to a number of implications that may be tested by further observations and experiments (see induction ; deduction ). If the conclusions drawn from the original hypothesis successfully meet all these tests, the hypothesis becomes accepted as a scientific theory or law; if additional facts are in disagreement with the hypothesis, it may be modified or discarded in favor of a new hypothesis, which is then subjected to further tests. Even an accepted theory may eventually be overthrown if enough contradictory evidence is found, as in the case of Newtonian mechanics, which was shown after more than two centuries of acceptance to be an approximation valid only for speeds much less than that of light. Role of Measurement and Experiment All of the activities of the scientific method are characterized by a scientific attitude, which stresses rational impartiality. Measurement plays an important role, and when possible the scientist attempts to test his theories by carefully designed and controlled experiments that will yield quantitative rather than qualitative results. Theory and experiment work together in science, with experiments leading to new theories that in turn suggest further experiments. Although these methods and attitudes are generally shared by scientists, they do not provide a guaranteed means of scientific discovery; other factors, such as intuition, experience, good judgment, and sometimes luck, also contribute to new developments in science. Branches of Specialization Science may be roughly divided into the physical sciences, the earth sciences, and the life sciences. Mathematics , while not a science, is closely allied to the sciences because of their extensive use of it. Indeed, it is frequently referred to as the language of science, the most important and objective means for communicating the results of science. The physical sciences include physics , chemistry , and astronomy ; the earth sciences (sometimes considered a part of the physical sciences) include geology , paleontology , oceanography , and meteorology ; and the life sciences include all the branches of biology such as botany , zoology , genetics , and medicine . Each of these subjects is itself divided into different branches—e.g., mathematics into arithmetic, algebra, geometry, and analysis; physics into mechanics, thermodynamics, optics, acoustics, electricity and magnetism, and atomic and nuclear physics. In addition to these separate branches, there are numerous fields that draw on more than one branch of science, e.g., astrophysics, biophysics, biochemistry, geochemistry, and geophysics. All of these areas of study might be called pure sciences, in contrast to the applied, or engineering, sciences, i.e., technology, which is concerned with the practical application of the results of scientific activity. Such fields include mechanical, civil, aeronautical, electrical, architectural, chemical, and other kinds of engineering ; agronomy, horticulture, and animal husbandry; and many aspects of medicine. Finally, there are distinct disciplines for the study of the history and philosophy of science. The Beginnings of Science Science as it is known today is of relatively modern origin, but the traditions out of which it has emerged reach back beyond recorded history. The roots of science lie in the technology of early toolmaking and other crafts, while scientific theory was once a part of philosophy and religion. This relationship, with technology encouraging science rather than the other way around, remained the norm until recent times. Thus, the history of science is essentially intertwined with that of technology. Practical Applications in the Ancient Middle East The early civilizations of the Tigris-Euphrates valley and the Nile valley made advances in both technology and theory, but separate groups within each culture were responsible for the progress. Practical advances in metallurgy, agriculture, transportation, and navigation were made by the artisan class, such as the wheelwrights and shipbuilders. The priests and scribes were responsible for record keeping, land division, and calendar determination, and they developed written language and early mathematics for this purpose. The Babylonians devised methods for solving algebraic equations, and they compiled extensive astronomical records from which the periods of the planets' revolution and the eclipse cycle could be calculated; they used a year of 12 months and a week of 7 days, and also originated the division of the day into hours, minutes, and seconds. In Egypt there were also developments in mathematics and astronomy and the beginnings of the science of medicine. Wheeled vehicles and bronze metallurgy, both known to the Sumerians in Babylonia as early as 3000 BC, were imported to Egypt c.1750 BC Between 1400 BC and 1100 BC iron smelting was discovered in Armenia and spread from there, and alphabets were developed in Phoenicia. Early Greek Contributions to Science The early Greek, or Hellenic, culture marked a different approach to science. The Ionian natural philosophers removed the gods from the personal roles they had played in the cosmologies of Babylonia and Egypt and sought to order the world according to philosophical principles. Thales of Miletus (6th cent. BC) was one of the earliest of these and contributed to astronomy, geometry, and cosmology. He was followed by Anaximander, who extended Thales' ideas and proposed that the universe is composed of four basic elements, i.e., earth, air, fire, and water; this theory was also taught by Empedocles (5th cent. BC) in Sicily. The philosophers Leucippus and Democritus (both 5th cent. BC) held that everything is composed of tiny, indivisible atoms. In the school founded at Croton, S Italy, by the Greek philosopher Pythagoras of Samos (6th cent. BC) the principal concept was that of number. The Pythagoreans tried to explain the workings of the universe in terms of whole numbers and their ratios; in addition to contributions to mathematics and philosophy, they also made notable studies in the area of biology and anatomy, e.g., by Alcmaeon of Croton (fl. c.500 BC). The most important developments in medicine were made by Hippocrates of Cos (4th cent. BC), known as the Father of Medicine, who formulated the science of diagnosis based on accurate descriptions of the symptoms of various diseases. The greatest figures of the earlier Greek period were the philosophers Plato (427-347 BC) and Aristotle (384-322 BC), each of whom exerted an influence that has extended down to modern times. Influence of the Alexandrian Schools The later Greek, or Hellenistic, culture was centered not in Greece itself but in Greek cities elsewhere, particularly Alexandria, Egypt, which was founded in 332 BC by Alexander the Great. The so-called first Alexandrian school included Euclid (fl. c.300 BC), who organized the axiomatic system of geometry that has served as the model for many other scientific presentations since then; Eratosthenes (3d cent. BC), who made a remarkably accurate estimate of the size of the earth; and Aristarchus (3d cent. BC), who showed that the sun is larger than the earth and suggested a heliocentric model for the solar system. Archimedes (287-212 BC) worked at Syracuse, Sicily, and made contributions to mathematics and mechanics that were surprisingly mo