The consistency condition which demands that new hypotheses agree with accepted theories is unreasonable because it preserves the older theory, and not the better theory. Hypotheses contradicting well-confirmed theories give us evidence that cannot be obtained in any other way. Proliferation of theories is beneficial for science, while uniformity impairs its critical power. Uniformity also endangers the free development of the individual.In other words, every time we reject theories that are inconsistent with older, more "established" theories, we make logical fallacies known as "appeal to antiquity," which falsely asserts that older theories are better theories.
We can clearly see why we do not want such consequences in science; if Theory B is rejected because Theory A came first, then in a world where Theory B was discovered first Theory A would have been rejected. The validity of a theory is replaced with its age. Although this might be an oversimplification of the issue, the crux of the matter still holds.
A recent example of this deals with the field of crystallography. As I mention in another blog Synthesis of Symmetry, the Crystallographic Restriction Theorem, proven mathematically, states that a periodic solid, which is ordered on a microscopic level, can only have 2-fold, 3-fold, 4-fold or 6-fold rotational symmetries.
(A typical snowflake is seen to have a 6-fold symmetry.)
This Theorem has been established and accepted by scientists everywhere, and has been heralded as a fact. However, Dan Shechtman and his team in 1984 discovered and argued for the existence of quasicrystals (or quasiperiodic crystals) that have rotational symmetries of other degrees. At first his paper and his theory had been rejected by almost the entire scientific community; scientists who had taken the original Theorem to heart had tried to discredit the new, rising theory in every way possible. As Shechtman said, "For a long time it was [him] against the world."
But eventually, Shechtman had been successful in persuading the rest of the scientific community that quasicrystals do exist, and that the Theorem is at least incomplete, and that crystals with other forms of symmetry do exist. (He subsequently received a Nobel Prize for his work in 2011.) Had we not explored the new concept and stuck with the "older is better" mindset, such revolutions in scientific history would never have occurred.
In fact, Feyerabend argues that there are areas in science where pluralistic thinking is necessary for the discovery of facts. He cites the example of Brownian particles, which are perpetual motion machines of the second kind (meaning that they constantly and spontaneously converts thermal energy into kinetic energy). The fact that this violates the second law of thermodynamics cannot be observed directly; he argues that the measurements needed to show it directly are "beyond experimental possibilities" of the status quo. Thus we can see how considering other scenarios and hypotheses-- in this case, for example, an alternative theory of heat-- can be vital in the discovery of facts.
Such anarchistic and pluralistic approaches to science have been historically shown to be fundamental in the search for facts. They are they only ways for us to see just how incomplete are the theories that we "know" of now.