Many people think that science progresses in a linear fashion, from ignorance to knowledge. If that were true, old ideas would never need to be overturned, only built upon. 

Normal science means the study based on the previous scientific knowledge that is learned through textbooks and formal education. These textbooks:

• Outline the main questions of a field and 
• Give methods to answer them. 

Scientists are happy to refer to past achievements without assuming they are necessarily correct. Therefore, science should be kept objective and open-ended. 

Paradigms are at the heart of normal science. A paradigm is a collection of interconnected beliefs we use to understand the world. But it is a limited process. 

Scientific discoveries become paradigms when they are remarkable enough to attract a loyal following but still leave questions and unsolved problems for followers. 

Because there is a paradigm doesn’t mean there is a set of rules that accompany it. Historians can generally find the paradigms of a given community, but finding the specific rules that the community followed is more difficult because:

• Scientists may follow the same paradigm yet disagree on how to interpret it. 
• Scientists have experience and knowledge they don’t communicate clearly or don’t realise others lack.

One of the major functions of normal science is to solve anomalies. However, scientists often assure themselves there is a solution within the paradigm, and it must just be found. But this isn’t always the case. 

Crises are a necessary precondition for the emergence of novel theories. Sometimes we have to discard scientific ideas that we find comfortable because the problems they tried to fix did not work. 

A paradigm will become messy as people try to expand their existing views outward into new, creative directions. 

A crisis can end if:

• It is resolved within the existing and accepted paradigm.
• The problem is categorically explained but without the technology necessary to test the ideas fully. The community postpone their inquires to the future when technology has progressed.
• A new proponent arises that changes the paradigm. Competing views are fought out.

Almost every field has certain established beliefs and paradigms. It means that nearly anything could be subject to a crisis.

When a paradigm changes, almost the entire world changes with them. Scientists ask different questions, follow different rules and use different terms.

Scientific revolutions only go one way and are irreversible. A scientist who now views the world through a Copernican paradigm can’t go back to Ptolemy. 

Normal science is commonly held conclusions. When scientific revolutions occur, they can be invisible and hard to detect, but they are of crucial importance. 

A person will only change their mind about a scientifically held belief from an old paradigm through repeated testing.