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Theory is a contemplative and rational type of abstract or generalizing thinking, or the results of such thinking. Depending on the context, the results might for example include generalized explanations of how nature works. The word has its roots in ancient Greek, but in modern use it has taken on several different related meanings. A theory is not the same as a hypothesis. A theory provides an explanatory framework for some observation, and from the assumptions of the explanation follows a number of possible hypotheses that can be tested in order to provide support for, or challenge, the theory. A theory can be ''normative'' (or prescriptive), meaning a postulation about what ought to be. It provides "goals, norms, and standards". A theory can be a body of knowledge, which may or may not be associated with particular explanatory models. To theorize is to develop this body of knowledge. As already in Aristotle's definitions, theory is very often contrasted to "practice" (from Greek ''praxis'', πρᾶξις) a Greek term for "doing", which is opposed to theory because pure theory involves no doing apart from itself. A classical example of the distinction between "theoretical" and "practical" uses the discipline of medicine: medical theory involves trying to understand the causes and nature of health and sickness, while the practical side of medicine is trying to make people healthy. These two things are related but can be independent, because it is possible to research health and sickness without curing specific patients, and it is possible to cure a patient without knowing how the cure worked.〔See for example Hippocrates (Praeceptiones, Part 1 ). 〕 In modern science, the term "theory" refers to scientific theories, a well-confirmed type of explanation of nature, made in a way consistent with scientific method, and fulfilling the criteria required by modern science. Such theories are described in such a way that any scientist in the field is in a position to understand and either provide empirical support ("verify") or empirically contradict ("falsify") it. Scientific theories are the most reliable, rigorous, and comprehensive form of scientific knowledge,〔(【引用サイトリンク】first=Steven D. )〕 in contrast to more common uses of the word "theory" that imply that something is unproven or speculative (which is better characterized by the word 'hypothesis'). Scientific theories are distinguished from hypotheses, which are individual empirically testable conjectures, and scientific laws, which are descriptive accounts of how nature will behave under certain conditions. == Ancient uses == The English word ''theory'' was derived from a technical term in philosophy in Ancient Greek. As an everyday word, ''theoria'', , meant "a looking at, viewing, beholding", but in more technical contexts it came to refer to contemplative or speculative understandings of natural things, such as those of natural philosophers, as opposed to more practical ways of knowing things, like that of skilled orators or artisans.〔The word "theory" was used in Greek philosophy, for example, that of Plato. It is a statement of how and why particular facts are related. It is related to words for "spectator", ''thea'' "a view" + ''horan'' "to see", literally "looking at a show". See for example (dictionary entries at Perseus website ).〕 The word has been in use in English since at least the late 16th century. Modern uses of the word "theory" are derived from the original definition, but have taken on new shades of meaning, still based on the idea that a theory is a thoughtful and rational explanation of the general nature of things. Although it has more mundane meanings in Greek, the word apparently developed special uses early in the recorded history of the Greek language. In the book ''From Religion to Philosophy'', Francis Cornford suggests that the Orphics used the word "theory" to mean 'passionate sympathetic contemplation'. Pythagoras changed the word to mean a passionate sympathetic contemplation of mathematical knowledge, because he considered this intellectual pursuit the way to reach the highest plane of existence. Pythagoras emphasized subduing emotions and bodily desires in order to enable the intellect to function at the higher plane of theory. Thus it was Pythagoras who gave the word "theory" the specific meaning which leads to the classical and modern concept of a distinction between theory as uninvolved, neutral thinking, and practice.〔Russell, Bertrand, ''History of Western Philosophy''〕 In Aristotle's terminology, as has already been mentioned above, theory is contrasted with ''praxis'' or practice, which remains the case today. For Aristotle, both practice and theory involve thinking, but the aims are different. Theoretical contemplation considers things which humans do not move or change, such as nature, so it has no human aim apart from itself and the knowledge it helps create. On the other hand, ''praxis'' involves thinking, but always with an aim to desired actions, whereby humans cause change or movement themselves for their own ends. Any human movement which involves no conscious choice and thinking could not be an example of ''praxis'' or doing.〔The LSJ cites two passages of Aristotle as examples, both from the ''Metaphysics'' and involving the definition of natural science: (11.1064a17 ), "it is clear that natural science (φυσικὴν ἐπιστήμην) must be neither practical (πρακτικὴν) nor productive (ποιητικὴν), but speculative (θεωρητικὴν)" and (6.1025b25 ), "Thus if every intellectual activity () is either practical or productive or speculative (θεωρητική), physics (φυσικὴ) will be a speculative () science". So Aristotle actually made a three way distinction between practical, theoretical and productive or technical - or between doing, contemplating or making. All three types involve thinking, but are distinguished by what causes the objects of thought to move or change.〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Theory」の詳細全文を読む スポンサード リンク
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