A theory is distinct from a mere scientific explanation.  Scientific explanation requires a causal explanation, which requires a law-governed explanation.  Natural law describes but does not explain natural phenomena.  Newton’s law of universal gravitation described, but did not explain, what caused gravitational attraction.  Theories unify empirical regularities and describe the underlying process that accounts for these phenomena.  Within theories are axioms, a small set of postulates, which are not proved in the axiom system but assumed to be true.[1]

A theory goes beyond natural laws and scientific explanations in explaining the scientific explanations. A theory refers to a body of explanatory hypotheses for which there is strong support.[2]  Theories are a conjunction of axioms (of the laws of nature) and correspondence of rules specified in a formalized ideal language.  This ideal language is composed of three parts: logical terms, observational terms, and theoretical terms.  The logical terms were initially treated as analytic claims (particularly under the hypothetico-deductive model).  Observational claims were to be unproblematic, understood as referring to incorrigible sense-data and later to publicly available physical objects.  Correspondence rules were used to connect theoretical language to observational claims.[3]