Running through science there is a duality in the description of systems, which has resulted in some of the deepest problems of scientific method and analysis. This duality arises from the analytical procedure which reduced all complex, macroscopic systems to a set of simpler, microscopic components. Natural processes are thus regarded as having two sides: a macroscopic or phenomenological one, which is observed directly; and a microscopic one, which may not be directly observable but which is postulated to underlie and in some sense explain the macroscopic process.