Science (from the Latin scientia, meaning "knowledge") is in its broadest sense to any systematic knowledge-base or prescriptive practice that is capable of resulting in a prediction or predictable type of outcome. In this sense, science may refer to a highly skilled technique or practice.

In its more restricted contemporary sense, science is a system of acquiring knowledge based on scientific method, and to the organized body of knowledge gained through such research.This article focuses on the more restricted use of the word. Science as discussed in this article is sometimes called experimental science to differentiate it from applied science, which is the application of scientific research to specific human needs—although the two are commonly interconnected.

Science is a continuing effort to discover and increase human knowledge and understanding through disciplined research. Using controlled methods, scientists collect observable evidence of natural or social phenomena, record measurable data relating to the observations, and analyze this information to construct theoretical explanations of how things work. The methods of scientific research include the generation of hypotheses about how phenomena work, and experimentation that tests these hypotheses under controlled conditions. Scientists are also expected to publish their information so other scientists can do similar experiments to double-check their conclusions. The results of this process enable better understanding of past events, and better ability to predict future events of the same kind as those that have been tested.

Basic classifications

Scientific fields are commonly divided into two major groups: 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 tested for its validity by other researchers working under the same conditions.There are also related disciplines that are grouped into interdisciplinary and applied sciences, such as engineering and health science. Within these categories are specialized scientific fields that can include elements of other scientific disciplines but often possess their own terminology and body of expertise.

Mathematics, which is classified as a formal science, has both similarities and differences with the natural and social sciences. 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.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 empirical sciences. The formal sciences are essential in the formation of hypotheses, theories, and laws, both in discovering and describing how things work (natural sciences) and how people think and act (social sciences).
History and etymology

While empirical investigations of the natural world have been described since antiquity (for example, by Aristotle, Theophrastus and Pliny the Elder), and scientific methods have been employed since the Middle Ages (for example, by Ibn al-Haytham, Abu Rayhan Biruni and Roger Bacon), the dawn of modern science is generally traced back to the early modern period, during what is known as the Scientific Revolution of the 16th and 17th centuries.

The word "science" comes through the Old French, and is derived in turn from the Latin scientia, "knowledge", the nominal form of the verb scire, "to know". The Proto-Indo-European (PIE) root that yields scire is *skei-, meaning to "cut, separate, or discern".Similarly, the Greek word for science is 'ep?st?µ?', deriving from the verb 'ep?staµa?', 'to know'. From the Middle Ages to the Enlightenment, science or scientia meant any systematic recorded knowledge.Science therefore had the same sort of very broad meaning that philosophy had at that time. In other languages, including French, Spanish, Portuguese, and Italian, the word corresponding to science also carries this meaning.

Prior to the 1700s, the preferred term for the study of nature was natural philosophy, while English speakers most typically referred to other philosophical disciplines (such as logic, metaphysics, epistemology, ethics and aesthetics) as moral philosophy. Today, "moral philosophy" is more-or-less synonymous with "ethics". Far into the 1700s, science and natural philosophy were not quite synonymous, but only became so later with the direct use of what would become known formally as the scientific method. By contrast, the word "science" in English was still used in the 17th century (1600s) to refer to the Aristotelian concept of knowledge which was secure enough to be used as a sure prescription for exactly how to do something. In this differing sense of the two words, the philosopher John Locke wrote disparagingly in 1690 that "natural philosophy is not capable of being made a science".

Locke was to be proven wrong, however. By the early 1800s, natural philosophy had begun to separate from philosophy, though it often retained a very broad meaning. In many cases, science continued to stand for reliable knowledge about any topic, in the same way it is still used in the broad sense (see the introduction to this article) in modern terms such as library science, political science, and computer science. In the more narrow sense of science, as natural philosophy became linked to an expanding set of well-defined laws (beginning with Galileo's laws, Kepler's laws, and Newton's laws for motion), it became more popular to refer to natural philosophy as natural science. Over the course of the nineteenth century, moreover, there was an increased tendency to associate science with study of the natural world (that is, the non-human world). This move sometimes left the study of human thought and society (what would come to be called social science) in a linguistic limbo by the end of the century and into the next.

Through the 1800s, many English speakers were increasingly differentiating science (i.e., the natural sciences) from all other forms of knowledge in a variety of ways. The now-familiar expression “scientific method,” which refers to the prescriptive part of how to make discoveries in natural philosophy, was almost unused until then, but became widespread after the 1870s, though there was rarely total agreement about just what it entailed.The word "scientist," meant to refer to a systematically-working natural philosopher, (as opposed to an intuitive or empirically-minded one) was coined in 1833 by William Whewell.Discussion of scientists as a special group of people who did science, even if their attributes were up for debate, grew in the last half of the 19th century.Whatever people actually meant by these terms at first, they ultimately depicted science, in the narrow sense of the habitual use of the scientific method and the knowledge derived from it, as something deeply distinguished from all other realms of human endeavor.

By the twentieth century (1900s), the modern notion of science as a special kind of knowledge about the world, practiced by a distinct group and pursued through a unique method, was essentially in place. It was used to give legitimacy to a variety of fields through such titles as "scientific" medicine, engineering, advertising, or motherhood. Over the 1900s, links between science and technology also grew increasingly strong.