: Read the following passage and answer the four questions that follow.

The standard story of how scientific revolutions occur tells us that an established paradigm collapses under the weight of accumulated anomalies, and a new framework, more accurate and more elegant, replaces it. This story is reassuring because it makes the transition look rational; the old picture failed empirically, and the community of scientists, being empirical, switched. Yet historians of science have for some time pointed out a curious feature of major theoretical shifts. The crucial anomalies are very often known long before the paradigm is overthrown, and the eventual replacement is frequently no better at handling them, at least at first, than the theory it displaces. Galileo’s heliocentrism initially required ad hoc patches to explain motions that geocentric astronomy already explained reasonably well, and the early atomic theory could not predict valences with the precision of the contemporary chemistry of equivalents. If anomalies alone do not topple paradigms, what does?

One tempting answer is that paradigms fall when a more elegant framework arrives. Elegance, however, is not a property paradigms simply have or lack; it is something they acquire through the practice of those who use them. Newtonian mechanics was thought clumsy until the calculus of variations made it lean. Elegance, then, is partly a record of accumulated mathematical labour, and so cannot, without circularity, be the reason a new paradigm is preferred.

A more persuasive account locates the shift in the changing distribution of authority within scientific communities. Young researchers, looking for problems on which to make a reputation, drift toward the new framework because it offers more open questions and fewer entrenched experts. As they

secure positions and prizes, the institutional centre of gravity moves. The transition therefore looks empirical in retrospect, but is sustained at the time by something closer to a generational migration. This is not to say that evidence is irrelevant. It is to say that the community will tolerate evidence weighing against a young theory and refuse the same indulgence to an old one.

Such an account is uncomfortable, because it suggests that what is called scientific consensus is partly an artefact of professional life. Yet to call this a critique of science would be to misread it. The migration of attention to richer research problems is precisely what makes science productive. If young scientists clung to a paradigm only because it was well-confirmed, no new framework, however promising, could attract the labour needed to develop it. The scientific community’s apparent injustice toward incumbent theories is the price it pays for being able to move at all. A theory is overthrown not when it has been refuted but when it has stopped being interesting to those who still have careers to build.