They are highly technical words so scientists and engineers should be cautious when using them.

Several times in our engineering study, we encounter words which seem to be defined the same. Worlds like fact, law, theory, and hypothesis, they have been introduced in our high school science subjects and encounter them in engineering school. Because they are commonly used terms in engineering, they are printed in textbooks and used by professors in class.

And yet we confuse them with each other, so we use such words interchangeably. Their true, scientific definitions have been neglected through time because they are used colloquially. While that is not considered a sin for science and engineering students, it pays to know the differences of the words’ meanings.

So what is a fact? What is a law? What is a theory? What is a hypothesis?

In the context of everyday language, the use of such words is regardless of their scientific meanings.

People use the word ‘fact’ to refer to something that is true, which denotes a strong stand. “That’s a fact! You cannot deny that,” some would say. Using the word ‘law’ informally or outside of politics means almost the same with fact. There is also a common use with the word ‘theory’ to refer to a supposition or an assumption. “I have a theory that Rick will die in the next season.” Something like that. It may or may not be true, but it is often based on observation or a gut feeling. Meanwhile, the word ‘hypothesis’ is a lot like theory, but only used by people who want to sound smart.

While the misuse of those four words in casual conversations is forgivable, such words are never to be mixed up in the fields of science and engineering. They are highly technical words so scientists and engineers should be cautious when using them.

The word fact is generally what it is when used in the technical language, except that it is very specific. I could say, “I have dropped a ball, so it is a fact that it will fall to the ground.” In this sense, fact is not really the word. The term used in science for fact is “observation”.

A hypothesis, on the other hand, is an untested statement about nature or an educated guess. This is an idea that is formulated to explain observations in a logical way. But one cannot easily make a good hypothesis without it being testable – it should be predictive about what would happen in similar situations. It can never be verified nor refuted, else it becomes a theory.

When a hypothesis has withstood all attempts to falsify it, it becomes a theory. The word ‘theory’ refers to a well-tested, usually mathematical, model of some part of science. When used in physics, it usually takes the form of an equation or a group of equations, complete with guides on how to utilize such. A theory is a well-substantiated explanation acquired through the scientific method and repeatedly tested and confirmed through observation and experimentation. It has never shown to be false despite the many attempts to break it. Examples of this are the electromagnetic field theories and the structural theories.

Meanwhile, a law is a statement, usually mathematical, that describes the relation between variables in some particular physical phenomena. It is a descriptive generalization about how aspects of the natural world behave under stated circumstances. A law is a proof that something happens and how it happens, but not why it happens. Say the Laws of Thermodynamics and the Law of Universal Gravitation.

Never have to make the mistake of using them outside of their scientific meanings, engineer. Unless of course you’re just taking to someone about The Walking Dead, then you can safely say the quote I already mentioned: “I have a theory that Rick will die in the next season.”

Sources: Life Hacker | Futurism | Exposing PseudoAstronomy