Illustrated · 1 min
Image source: By Sylvia Freeman
It can be easy to mix up law and theory, so make sure you're clear about what a theory is.
Read · 1 min
A common misconception is that a hypothesis can turn into a theory, and theories turn into laws with enough evidence. However, each one of these is a distinct component of the scientific method.
As stated by the University of California, "Hypotheses, theories, and laws are rather like apples, oranges, and kumquats: One cannot grow into another, no matter how much fertilizer and water are offered."
A scientific law describes a certain event of the natural world, but it does not attempt to explain how the event occurs. It is simply a result of repeated observations and is based on empirical data (experimental evidence). For this reason, a law can serve as a foundation for making a hypothesis or developing a theory for how or why something happens.
Video
by Matt Anticole on TED-Ed
Is a theory the same as a law? In this video, you'll learn about how these words are different and why they can't be used interchangeably.
Illustrated · 2 min
A law describes an event, but it does not explain why the event happens. Laws describe relationships, specific situations, and conditions. This is different from a principle, which tells us why and how things happen.
There are many laws of nature in the scientific world. You've probably heard of one called gravity. Isaac Newton developed his law of gravity in the 17th century. It describes how objects are influenced by forces pulling on them. If you drop an apple, it will fall. If you throw an apple in the air, it will follow a specific path while falling down. Newton's laws don't tell us why the apple falls or what causes it to fall, just that it does fall.
Similarly, the law of conservation of mass says that mass can't be created or destroyed. It doesn't say why this is true, neither does it say how it is true. It just says what happens—mass is always conserved.
Scientific laws can be written as mathematical equations, so they are called quantitative. However, there aren't very many laws in biology. They are more common in physics and chemistry.
Image source: By Orion 8 CC BY-SA 3.0, via Wikimedia Commons
Principles are ideas based on scientific rules and laws that are generally accepted by scientists. They are fundamental truths that are the foundation for other studies. Principles are qualitative.
They aren't really rules that can be written down with mathematical symbols. They are more like widely accepted ideas that scientists use to make predictions and develop new laws.
Principle of Relativity: Physical laws take the same form in all systems of reference. (Albert Einstein)
Principle of Special Relativity: The speed of light is the same for all observers. (Albert Einstein)
Pauli Exclusion Principle: No two particles with the same quantum numbers can be at the same position in space and time. (Wolfgang Pauli)
Sometimes, people say that a law is the same as a principle, and vice versa. This is because both result in reliable predictions of natural phenomena.
