"In their most unusual forms, however, probabilistic verification theories all have recourse to one or another of the pure neutral observation-languages discussed in Section X. One probabilistic theory asks that we compare a given scientific theory with all others that might be imagined to fit the same collection of observed data. Another demands the construction in imagination of all the tests that given scientific theory might conceivably be asked to pass.  Apparently some such construction is necessary for the computation of specific probabilities, absolute or relative, and it is hard to see how such a construction can possibly be achieved. If, as I have already urged, there can be no scientifically or empirically neutral system of language or concepts, then the proposed construction of alternate tests and theories must proceed from one or another paradigm-based tradition. Thus restricted it would have no access to all possible experiences or to all possible theories. As a result, probabilistic theories disguise the verification situation as much as they illuminate it. Though that situation does, as they insist, depend upon the comparison of theories and of much wide-spread evidence, the theories and observations at issue are always closely related to ones already in existence. Verification is like natural selection: it picks out the most viable among the actual alternatives in a particular historical situation. Whether that choice is the best that could have been made if still other alternatives had been available or if the data had been of another sort is not a question that can usefully be asked. There are no tools to employ in seeking answers to it."
 For a brief sketch of the main route to probabilistic verification theories, see Ernest Nagel, Principles of the Theory of Probability, Vol. 1, No. 6, of International Encyclopedia of Unified Science, pp. 60-75.
From: “The Resolution of Revolutions”, Chapter XII in Thomas S. Kuhn, The Structure of Scientific Revolutions, Second Edition, Enlarged. Chicago, University of Chicago Press, 1970.
Reader Note: When we moved into our new house several years ago, I was reunited with all my old books, including college texts such as Kuhn's work, which had been in storage for a number of years. Re-reading the section above, it immediately became apparent why I had not missed it. Astonishingly, I actually read this book once -- the whole thing -- it is even underlined -- and I recall being examined on it on two occasions. I have bolded certain passages for my (and I hope your) enjoyment because they seem particularly portentous without making a great deal of sense to me. I was so much older then, I'm younger than that now. Or something like that.
6-4-11 Tulsa, Oklahoma
6-5-11, Nashville, Tennessee
Duck-Rabbit (used by Thomas S. Kuhn to illustrate the concept of "paradigm shift")