Thomas Kuhn's Theory of Scientific Revolutions

1. "Normal Science", that is to say everyday, bread-and-butter science, is a "puzzle-solving" activity conducted under a reigning "paradigm".
   
   
   • The paradigm is the example or model of a great scientific achievement (such as Newton's theory of gravity, or Einstein's theory of relativity) which provides an inspiration and a guide showing how to do scientific research. It is not quite an explicit set of rules and regulations (not a recipe or formula), but it does clearly "show the way".
   • "Puzzle solving" is the normal or everyday activity of scientists, and consists of problems which are believed, in advance, to have a solution, if only enough ingenuity and effort is brought to bear, using the paradigm as a guide.
     
     
2. An "anomaly" arises when a puzzle, considered as important or essential in some way, cannot be solved. The anomaly cannot be written off as just an ill-conceived research project; it continues to assert itself as a thorn in the side of the practicing scientists. The anomaly is a novelty that cannot be written off, and which cannot be solved. Examples of anomalies include:
   
   
   • According to Newtonian mechanics, there should be a difference in the speed of light when it is issued from a moving source. Careful experiments in the late 19th century found no such difference, despite the most accurate of instruments.
   • According to the Theory of the special creation of species, a divine being created each species separately and individually, perfectly adapted to its environment. The discovery of the fossil remains of species not corresponding to any existing species (extinct species) contradicted this key assumption of biology before Darwin.
     
     
3. This opens up a period called the "crisis", during which time new methods and approaches are permitted, since the older ones have proved incapable of rising to the task at hand (solving the anomaly). Views and procedures previously considered heretical are temporarily permitted, in the hope of cracking the anomaly.
   
   
4. One of these new approaches is successful, and it becomes the new paradigm through a "paradigm shift". This constitutes the core of the scientific revolution.
   
   
5. The new paradigm is popularized in text-books, which serve as the instruction material for the next generation of scientists, who are brought up with the idea that the paradigm -- once new and revolutionary -- is just the way things are done. The novelty of the scientific revolution recedes and disappears, until the process is begun anew with another anomoly-crisis-paradigm shift.