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Science, systematic study of nature and of individual and social human behavior. Science is distinguished from other intellectual disciplines, like the arts and humanities, by several key characteristics. It is based upon observation, either by the unaided senses or with the help of instruments that increase the power of the senses, like microscopes or telescopes. Science requires the careful collection and organization of data. Above all, science employs a rigorous method of reasoning about what it observes. The scientific method relies upon logic to draw conclusions from evidence and tests its reasoning with experiments. As study progresses, a larger pattern or underlying law begins to emerge that helps explain phenomena like the formation of gases, the motion of planets, or the division of cells. Scientists attempt to state those laws or patterns in the form of theories or hypotheses, and those statements are also subjected to experiments. Some hypotheses prove useful and enduring, others are refuted or superseded by new experiments or new findings. Finally, science expresses itself mathematically, in formulas that state numerically the dynamics or relations underlying what we see. Neither the arts nor the humanities are rigorous in the way that science is; the questions they ask, the methods they use, and their findings and results are different.

The scope of science is vast. It is broken up into a great many fields and specialties. But a few major divisions are still useful for an overview. The physical sciences are, historically, probably the oldest and include astronomy, meteorology, chemistry, physics, and geology. These fields cover inanimate nature. Life and living beings are studied by the life sciences, including biology, zoology, botany, physiology, and paleontology. The social sciences study human beings as they reveal themselves in individual behavior and in society and its institutions. Such studies include political science, economics, psychology, anthropology, and sociology. To the extent that these disciplines are less successful than the natural sciences in expressing their findings mathematically, they have been criticized for lacking the rigor of pure science. Finally, although they are not themselves sciences in the strict sense, mathematics and logic are essential to science. Though in many ways the two overlap, mathematics provides science with symbols and procedures for measuring and for calculating relations. Logic discovers the ratio and procedures of accurate reasoning.

The development of science has led to an explosion of knowledge unprecedented in human history. Allied with mechanical ingenuity, it led to technology, the application of scientific knowledge to practical problems. The results have completely transformed the world. In partnership with modern industry, finance, and the state, science has produced a mixed legacy, creating tools that heal and destroy, that enhance life and threaten it with annihilation.


Science's earliest manifestation was among the Greeks who were the first people to reason logically about the natural world. Instead of accepting occult explanations for what they observed, the Greeks tried to discover intelligible laws underlying things. They developed logic and mathematics and made impressive contributions to human knowledge. In the 4th century B.C., Hippocrates laid down elementary principlesforthe practice of medicine. One hundred years later, Aristotle attempted an exhaustive classification of phenomena based upon logical categories and direct observation. Euclid and Archimedes were great mathematicians and Ptolemy's description of the motion of the planets would not be improved upon for nearly 1,500 years.

With the fall of the Roman Empire and the onset of the Middle Ages in the West, it was left to Islam to pursue some of the promise of the Greeks. To mention only a few great Muslim thinkers, Alhazan in optics, Aricanna in medicine, and Al-Khwarizmi in algebra made important contributions that had their greatest impact on Christian Europe in the late Middle Ages. Schooled in logical rigor by the Scholastics and with access to Islamic work and the Hindu-Arabic numerical notation, Europe was ripe for intellectual change. It came first in Italy between the 14th and 16th centuries in the Renaissance. The use of perspective in painting and architecture that explored principles laid down by the Greeks and Romans fostered a spirit of inquiry that led to detailed studies of human anatomy and innovations in mechanics and virtually every branch of human knowledge. Men like Galileo and da Vinci pointed the way for the rest of Europe. Nicolaus Copernicus, the Polish astronomer, put an end to the medieval view of the world with his theory, based upon careful telescopic observation, that the earth was not the center of the universe but only one of several planets that revolves around the sun. The Copernican revolution sent profound shock waves throughout Europe, and combined with the impact of the discovery of the Americas, inspired the best minds of Europe to turn to science.

In the 17th century, Descartes in France laid the philosophical foundations of the scientific method. In the same century, the Englishman Newton and the German Leibniz simultaneously discovered calculus, and Newton wrote the Principia Mathematica in which he proposed his law of universal gravitation. His countryman, William Harvey, described the circulation of blood and Robert Boyle advanced the science of chemistry.

Building upon the work of the previous century, the 18th century saw rapid advances. In chemistry came the discoveries of gases, among them chlorine, hydrogen, and carbon dioxide. Carolus Linnaeus developed a system for the classification of animals and Luigi Galvani, Alessandro Volta, and Benjamin Franklin made advances in the study of electricity. In addition, the sciences had an impact outside of the laboratory in the rationalisms and skepticism of Voltaire, Hume, Diderot, and the work of Adam Smith, whose Wealth of Nations marked the advent of the modern study of economics. In the 19th century, Darwin did his pioneering work on natural selection and evolution, presenting theories that would have almost as profound an effect upon social and political thought as they did in science. Michael Faraday and Joseph Henry pioneered work in electromagnetism. James Clark Maxwell studied the laws of electricity and magnetism, and great advances were made in modern medicine, typified by the work and career of Louis Pasteur. Progress in medicine and in the care and treatment of the sick led to a dramatic increase in life expectancy.

Much of the early optimism felt about science began to be lost in the era of World War I, a grim demonstration of what the new knowledge and technology could do when applied to war. But the decades between World War I and World War II saw perhaps the most fertile and creative years of 20th-century science with the work of Einstein, who proposed his theory of relativity, as well as Max Planck and Nils Bohr, who deepened our understanding of the structure and mechanics of the atom. It was their work that made possible the creation of the atomic bomb, a weapon which revolutionized both war and peace.

In the latter half of the 20th century, science has become a highly complex and competitive intellectual pursuit, engaging the talents of many of the best minds throughout the world and tackling problems as diverse as the origin's of the universe to the perfecting of high-definition TV or the next generation of high-speed computers. Modern science is pursued almost entirely in the laboratories of universities, governments, or private industries, and research and development commands billions of dollars every year. But no matter how large or complex the facilities and supporting institutions, the basic work of science requires a combination of intellectual rigor, intuitive power, ambition, and a desire to know that are the characteristics of the individuals who pursue science.

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