A scientific theory or law represents a hypothesis that has been validated through repeated testing over many years.

• A theory is an explanation for a set of related phenomena, like the theory of evolution.
• The word "law" is often used to point to a specific mathematical equation that refers to the different elements within a theory. For example, Pascal's Law refers to the equation that describes the difference in pressure based on height.

Once a scientific theory is established, it is difficult to get the scientific community to abandon it.

Science philosopher Thomas Kuhn used the term scientific paradigm to explain a working set of concepts under which science operates. When one paradigm is overturned in favour of a new set of theories, the very nature of science changes.

Occam's Razor is a principle of the scientific method. It states that "entities should not be multiplied beyond necessity." It means that where two hypotheses are presented and have equal predictive power, the most simple explanation that fits the available data is the preferred hypothesis.

The appeal to simplicity has been adopted by most of science, as Albert Einstein expressed, "Everything should be made as simple as possible, but not simpler."