"One idea is truer than another if it allows us to explain and understand more of our experience.
The idea that the sun and stars move around the Earth explained only why they move across the sky, but the idea that the Earth orbits the sun while rotating on its axis is more true, because it explains also why we have seasons. Strictly speaking, however, we will never know whether the Earth really revolves around the sun; another, even truer, theory could conceivably come along.
In support of his view, James pointed out that in practice all scientific theories are approximations. Rarely, if ever, does one theory explain all the facts of experience. Instead, one theory often does well with one set of phenomena while the other theory does well with another set.
A scientific theory that explains more is truer than one that explains less, and the truer theory is preferred. Kuhn might add that even a paradigm that explains no more phenomena than a rival but explains those phenomena better is preferred—as for example Copernicus’ heliocentric model of the solar system was preferred to Ptolemy’s geocentric model, because Copernicus’ model was simpler and more elegant that the cumbersome epicycles of Ptolemy’s model, even though at the time the two models fitted astronomical data about equally well. If scientists prefer theories that explain more phenomena and paradigms that make more sense of our experience more plausibly, then the progress of science no longer seems so unreasonable. It is the result of selection, the exercise of scientists’ preference for theories and paradigms that make better sense of our experience."
Taken from the book "Understanding Behaviorism" by William M. Baum.