Richard J. Severson

One of the mind-blowing books I read as a college student was Thomas Kuhn’s The Structure of Scientific Revolutions (1962).  According to Kuhn, science does not evolve through a cumulative process—one discovery building upon another one—as most of us have been taught.  Instead, it evolves by means of revolutions that overturn old paradigms and create new ones. 

A scientific paradigm is a worldview that entails the theories, experimental equipment, and research agenda that is accepted by virtually all practitioners of a particular science, such as physics.  The paradigm is a human construct—a framework—that is imposed upon nature as a tool for understanding it, though it is never a perfect fit.  In what Kuhn calls “normal science,” scientists primarily work on the little discrepancies or puzzles that are a consequence of the imperfect fit of the paradigm to its subject matter.  The number of discrepancies grows as the precision of scientific investigations and instrumentation increases over time.  Eventually a crisis appears as the paradigm seems less and less able to resolve the growing number of problems.  Different versions of the paradigm are invented in order to try to fix things and salvage the paradigm.  Finally, a new paradigm emerges that seems better able to explain the discrepancies.  If advocates of the new paradigm persuade the majority of scientists to adopt its point of view, then the scientific revolution is successful, and a new period of normal science begins to investigate the puzzles of the new paradigm.     

Let me share a fairly well-known example of how this looks in real history.  In the 17^th century, the paradigm for understanding the chemistry of combustion revolved around the theory of phlogiston.  Phlogiston was thought to be a substance that combustible materials, like wood or air, contained.  When something was burned (combusted), the phlogiston was released and eventually the material would no longer be combustible because all the phlogiston was depleted.  This paradigm was very successful in explaining combustion—including its relationship to respiration and rusting—for decades.  But eventually the experimental data became overly problematic for the paradigm. When magnesium burned, for example, it was found to have gained mass rather than lose it as one would expect if phlogiston had been released from the magnesium.  How could that be?  In careful experiments with closed containers of air, Lavoisier and other chemists discovered a substance that at first they thought was dephlogisticated air.  Eventually this new substance was called oxygen, and a new paradigm for combustion emerged that focused on the consumption of oxygen instead of the release of phlogiston. 

It should be noted that these two paradigms regarding combustion were incompatible, even contradictory, which is the norm in scientific revolutions.  The “discovery” of oxygen didn’t just add another (cumulative) element to the growing edifice of scientific knowledge.  Instead, its discovery was embedded in a struggle between two paradigms about how combustion works.  Those scientists who abandoned the phlogiston paradigm were now operating in a different world where phlogiston could not even exist.  This is how scientific revolutions happen.  In fact, many of the scientists committed to the phlogiston paradigm refused to convert to the new paradigm.  This is another aspect of science that we don’t often hear about.  It can take a generation or more for a new paradigm to be widely accepted because, understandably, the older scientists had devoted their lives to the pursuits of normal science under the old paradigm. 

The tenacity with which scientists hold on to paradigms, even sometimes in the face of overwhelming contrary evidence, is actually one of the strengths of the scientific enterprise.  We don’t want paradigms to change easily, and it would be a mistake to think that dealing with contrary evidence is anything unusual.  That is the gist of normal science: persevering with the paradigm by investigating and explaining the puzzles of contrary evidence.  Changing paradigms is usually the work of younger scientists, or scientists new to a particular field, who lack the lifetime investment in the old paradigm.  Think of Einstein who published three revolutionary papers in 1905 when he was a young man working in a patent office (he couldn’t even find a job in his field of theoretical physics). 

Another point worth mentioning about shifting from one paradigm to another is that there is no neutral ground where one might stand and make a reasoned judgment about which paradigm is best.  It is not possible, in other words, to do science outside of the context of a paradigm.  If you think about it, what kind of research could you do if you didn’t have a theory about how something works, plus equipment with which to test your theory, plus a sense for what kind of questions would be worth investigating?  These are what the paradigm provides.  If every possible explanation about how nature works was equally plausible because there was no paradigm, it would also be equally arbitrary and impossible to investigate further.  How would you know that your research was successful unless you had a paradigm that told you what to expect and not expect in your research results? 

The phlogiston paradigm was real science even though it is meaningless in our time. This is why Kuhn used the term “conversion” when describing how scientists change allegiance to a new paradigm.  It is like leaving one world behind and entering another one.  Each world has its reasonableness and explanatory power.  But typically the new paradigm is a little more successful at explaining the problems that led to crisis, and scientists take the risk of entering into the new paradigm’s world (and rejecting the old one) mostly based upon the promise of better results in the future.