Paradigm shifts occur when a period of 'normal science' encounters significant 'anomalies' that cannot be reconciled within the existing paradigm, leading to a 'crisis'.

According to Kuhn, 'normal science' is the routine problem-solving activity conducted within an accepted paradigm. Scientists during this phase are not seeking to overturn fundamental theories but to extend and refine them, solving 'puzzles' that fit within the established framework. However, over time, observations or experimental results may emerge that contradict the paradigm's predictions – these are called 'anomalies'. Initially, anomalies are often ignored or explained away, but if they accumulate and become too persistent or significant, they can no longer be dismissed. The accumulation of severe anomalies leads to a state of 'crisis' within the scientific community. The existing paradigm is increasingly questioned, and confidence in its ability to explain phenomena erodes. During this crisis period, radical new theories and approaches are proposed, marking a revolutionary phase where competing frameworks vie for acceptance. The crisis is ultimately resolved when a new paradigm emerges that can explain the accumulated anomalies and offer new avenues for research, thus initiating a new period of normal science.