Today on social media I witnessed yet another confusion regarding the differences between the terms “law” vs “theory” vs “hypothesis.” These are thoroughly well-defined concepts in the world of scientific thought and research, but they don’t exactly match with our day-to-day interpretations of the words. So let’s take a quick look at them and breakdown the relationships between the three as they are used in professional publications and academic endeavors.

First, when you make a guess or a suggestion about how you think something might work, you have generated a HYPOTHESIS. Something along the lines of: “Considering an apple falls to the ground when I let go of it, I bet everything in the universe gets pulled towards each other in a similar manner.” A good hypothesis can be thought of as a potential explanation, sometimes vague and undefined, for the reality that we observe. It can be examined, deconstructed, analyzed, and tested to be proven right or wrong—upheld or discredited. If during this examination there is discovered significant evidence from multiple sources, methods, or institutes that proves it correct, it can spawn laws…

Something is a LAW only if it is a specific statement that is constantly seen to be true and can be expressed using mathematics. Something like: “F = G(m1xm2)/r^2.” That little discovery is known as the Law of Gravity, and has over and over (with absolutely no exceptions) been observed to matched how two objects in space are pulled together based on their mass and distance. The hypothesis of the apple falling to the ground was thoroughly examined and applied to other scenarios in astronomy and physics, and this law is a direct result of this analysis. Combining the expanded hypothesis with this law forms the backbone of a very important theory…

The highest form of scientific understanding is when a concept becomes a THEORY. A theory is a defining system of explanations that rose out of a strong hypothesis, supported by laws and consistent empirical data. In very simple terms, Newton’s Theory of Gravitation can be expressed: “We see apples fall, planets orbit, and gases collect around suns. There is a universal force that pulls all physical objects towards each other. The strength of this force changes depending on the relationship between the objects.” A theory can be disproved, improved, or even replaced, but it is the Final Evolution of an idea. It does not ever somehow become a law or fact (scientists don’t typically like to use the term “fact,” but we’ll talk about that later).

A law is not stronger or better than a theory; it is a compact and calculated statement, often an ingredient of a theory. Evolution by natural selection will never become a law. Evolution itself is already expressed in multiple laws (see Mendel’s Law of Segregation and the Law of Independent Assortment; generally these laws express how the genetic composition of offspring is different than the genes of its parents) and the Theory of Natural Selection explains how this happens again and again to change a population. This theory has been tested, attacked, and scanned thoroughly for problems across many decades, but it is currently our best model for describing the origin of species. It does not explain every single detail—which makes sense given the incredible scale of time required for it to operate—but every competing theory has been shown to be worse at explaining what we see in the physical world.

The word “fact” is usually only used by a scientist when expressing these things to laymen, since the general public often has trouble with these three terms. But no respected scientist will claim to another scientist that they have arrived at “fact.” They do their best to discover reality by coming up with hypotheses, calculating laws, and developing theories—all the while replacing erroneous information or filling in the gaps when better ideas are put forth (Newton’s 1687 Theory of Gravitation was for the most part supplanted by Einstein’s 1915 Theory of Relativity, which more thoroughly justifies our observations of the universe).

So remember: When someone says, “I have a theory about that,” the scientist in you should hear, “I have a hypothesis about that.” And when someone says, “Evolution is just a theory,” the scientist in you should hear, “Evolution is just a robust, logical, scientific model that is currently the most accurate way to explain our observable reality.”

Let the scientist in you speak out!