Normal science goes astray when it goes into crisis, when an anomaly is more than an anomaly . Kuhn talks about instances that make anomalies particularly pressing and notes that it usually takes several of these instances to provoke crisis . The anomalies become more recognized by the profession . The anomaly may exist on a key point of the theory and thus be recognized instantly . Anomalies build up .
Crises are necessary for the emergence of new theories .
Then efforts begin to get a new commitment . This period of paradigm shift has many similarities to the period before a paradigm is in place . Science in crisis generates many speculative theories . These speculations are often versions of the old paradigm . The period of paradigm shift looks similar to the pre-paradigm period in that there are many competing theories and methods of investigation .