Theory of principle

B. E. Conway, Theory of Principles of Electrode Processes, Ronald Press, New York (1964). 

Thermodynamics is what Einstein called a theory of principle , that is thermodynamics starts from empirically observed general properties and deduces from them results that apply to every case which presents itself without making any assumptions regarding the constituents. The universality of thermodynamics so impressed Einstein that he stated, It... 

Classical thermodynamics, as it is applied to materials, raises some interesting philosophical issues in scientific explanation since its theoretical foundations are free of any assumptions regarding the nature or the composition of matter. The lack of models for matter in classical thermodynamics is considered to be its unique strength by many authorities. Einstein s commentary on the subject illustrates the point, frequently emphasized in the literature. According to Einstein, theories that depend on assumptions regarding the nature of materials are theories of construction. Classical thermodynamics and the special theory of relativity, on the other hand, are theories of principle. About theories of principle Einstein [1950] states ... 

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