Theory is especially often contrasted to “practice” an Aristotelian concept which is used in a broad way to refer to any activity done for the sake of action, in contrast with theory, which does not need an aim which is an action. A classical example of the distinction between theoretical and practical uses the discipline of medicine: Medical theory and theorizing 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. In modern contexts, while theories in the arts and philosophy may address ideas and empirical phenomena which are not easily measurable, in modern science the term “theory”, or “scientific theory” is generally understood to refer to a proposed explanation of empirical phenomena, made in a way consistent with scientific method. Such theories are preferably 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. In this modern scientific context the distinction between theory and practice corresponds roughly to the distinction between theoretical science and technology or applied science. A common distinction sometimes made in science is between theories and hypotheses, with the former being considered as satisfactorily tested or proven and the latter used to denote conjectures or proposed descriptions or models which have not yet been tested or proven to the same standard. — Wikipedia
Metatheory is a theory whose subject matter is some theory. All fields of research share some meta-theory, regardless whether this is explicit or correct. In a more restricted and specific sense, in mathematics and mathematical logic, metatheory means a mathematical theory about another mathematical theory. — Wikipedia
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