What is a Scientific Law?
You’ve probably heard of scientific laws before. Maybe you’ve even learned about the Law of Thermodynamics in chemistry class, or used Newton’s Laws of Motion for a physics experiment. But what exactly is a scientific law, and what makes it different from things like theories and hypotheses?
A scientific law is basically a rule or set of rules to describe a series of measurable observations. For example, Newton’s Universal Law of Gravitation uses an equation to describe how objects are attracted to each other based on their mass and proximity. This law was based on his measured observations of falling objects and the movement of the planets. Many scientific laws are expressed in the form of mathematic equations, though they can also be expressed in words.
It’s a common misconception that hypotheses are upgraded to theories and theories are upgraded to laws as they gain more scientific support. In reality, these three concepts are related but distinct from one another.
The essential difference between scientific laws and scientific theories or hypotheses is that laws describe how a thing happens, not why it happens. Theories and hypotheses, on the other hand, are explanations for why the natural world works the way it does (though theories are far more broad and well-supported than hypotheses). Theories often explain laws and laws are sometimes used to support theories, but they are not the same thing.
In fact, far from being the “upgraded” version of a theory or hypothesis, laws are often a jumping off point for our scientific understanding of a subject. Scientists can observe and measure a natural phenomenon and create a law based on their findings without having any knowledge of the underlying causes.
For example, the monk Gregor Mendel came up with the Law of Segregation and Law of Independent Assortment to describe the patterns of inheritance he observed as he crossbred pea plants with different traits. Even though Mendel lived in the 19th century and had no inkling of DNA or modern genetics, he was able to generate a law to describe his observations. Mendel’s early laws provided a starting point for our modern scientific understanding of inheritance, and he is still known today as the “father of genetics”.
Although they don’t explain why natural phenomena occur, scientific laws are still a vital piece of the scientific process. Laws can be used to build and support theories, to jump-start our understanding of a new scientific subject, or even to make real world calculations. Newton’s Laws of Motion, for example, help us understand how cars and their passengers move in a car accident, which allows us to build safer cars.
Magnascan (artist). (2011). Peas Pod Pea [digital art]. Retrieved from