Theories are formed in the hope that they have explanatory power; and in the short term we properly evaluate them by this rigorous criterion. As they age their comparative explanatory power usually weakens as they are replaced by superior theories, and if we are wise our attention then turns to the evidence that these redundant theories provide of the problems they were designed to tackle, problems that may be present in phenomena or in experience that is hard to observe, but is denoted in the implied or the overall framework and theory, considered as one, that the author presented.

In other words, the residue that theory leaves to history is description.