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scientific lawa statement of a uniform connection between empirical phenomena, to the effect that whenever and wherever conditions of a specified kind A occur, then so will certain conditions of another kind B. A law is a universal conditional statement of the form ‘For any A, if A, then B’. Thus scientific laws are more than statements of fact, they make counterfactual claims, for example, that ‘all water heated to 100 °C at sealevel and normal pressure will boil’. As well as deterministic laws of this type there are also probabilistic laws of the form, ‘For any A, if A, then a certain probability (less than 1 but more than 0) of B.
Laws may be empirical, theoretical, or idealized in form (compare IDEAL TYPE). The generalization achieved by scientific laws is often only possible by the formulation of laws in idealized form, e.g. involving such notions as ‘frictionless surfaces’ or ‘perfect gases’, with auxiliary assumptions being required for general laws to be applied to concrete cases.
On one view (see COVERING-LAW MODEL), the existence of laws is a central defining feature of science and scientific explanations. Competing conceptions of SCIENCE, however, give more central emphasis to explanatory mechanisms and EXPLANATORY THEORIES, which may involve scientific laws but need not do so (see also SCIENTIFIC REALISM).