In philosophy of science, intertheoretic reduction occurs when a reducing theory makes predictions that perfectly or almost perfectly match the predictions of a reduced theory, while the reducing theory explains or predicts a wider range of phenomena under more general conditions.
Special relativity, for example, can be reduced to Newtonian mechanics for speeds far less than c. According to Alexander Rosenberg philosophers mostly these days believe that reduction between sciences is possible in principle but concepts we currently have do not allow reductions even in many cases in which natural sciences are involved, for instance from biology to chemistry.
Furthermore, there is the issue of by what criteria one judges one theory as more fundamental than another.
However, it has been argued that there are some phenomena (e.g. phase transitions and critical phenomena) that cannot be reductively explicated in terms of the "more fundamental" theory of statistical mechanics.
You can help Wikipedia by expanding it.This philosophy of science-related article is a stub.