Study Guide

Nature of Science - Law vs. Hypothesis vs. Theory

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Law vs. Hypothesis vs. Theory

Law. Hypothesis. Theory. If you're taking a science class, you are going to hear these three words a lot. We were thinking it would be nice if we were all on the same page about what they mean, so we can discuss them at parties and stuff. What? You don't like to talk about science vocabulary at parties? Weird…

Run-In With The Law

Let's start with a scientific law. Scientific laws describe some sort of phenomenon we have observed. Sometimes we'll see them in the form of a mathematical equation, other times not, but we'll always see a boatload of evidence tagging along. The only limitation to a scientific law is that it doesn't explain how the phenomenon works. Bummer.

The equation for the force of gravity is a great example of a law. It describes the phenomenon of our cell phone crashing into the ground when we let go of it, or the fact that the computer we're staring at isn't floating off into space. Look at it: . Just beautiful. What the law of gravity doesn't tell us, though, is why this happens, or what gravity actually is.

The Hypothesis: It's More Than An Educated Guess

Up next is the humble hypothesis. A hypothesis is like a testable explanation of stuff we've observed. The fact that it's testable means we can do an experiment to see if our hypothesis was correct. For example, maybe we observed that putting a little salt in our pasta water makes it boil faster. We could totally do an experiment to determine if this is actually true, or if we were just more patient in waiting for our mac n' cheese that day. The evidence we collect from our experiment will support or refute our hypothesis.

A hypothesis is usually focused on explaining something specific. Notice that our salty water hypothesis is just trying to explain one specific phenomenon. We're not trying to explain how atoms move when they're heated or how chemical reactions form new compounds with different boiling points. We save the complex explanations for theories.

Here's A Theory

Theories allow us to explain a broad range of observations and even make predictions. Fancy. Theories aren't born overnight, though. Just like laws, theories come from tons of empirical evidence and experiments whose results have been reproduced over and over and over again. Theories can even take a bunch of hypotheses that have already been supported by scientific evidence and give us a nice, overarching explanation for the lot of them.

Take the atomic theory, for example. It states that everything is made up of these little particles called atoms, which come in different forms called elements. We can use this theory to explain how ice becomes water, how gasoline becomes exhaust, or what in the name of ooze is happening here. Of course, atomic theory is backed up by countless experiments that have produced mountains of evidence to support the fact that we are made of carbon and the atoms in your ice cream are starting to move faster with each second that passes. Better catch that drip.

There's also the theory of evolution. This one explains, using boatloads of evidence from a bunch of different scientific fields, how species have changed over the course of billions of years. If you can turn that explanation into an equation, we'd love to see it, because it is one wildly complex process. Definitely a job for a theory.

The, Er, Evolution of Laws, Hypotheses, and Theories

So, are laws, theories, and hypotheses written in stone? Put your pickaxe away, because the answer is no. That's right, even scientific laws are subject to change. Since we're constantly adding to our scientific knowledge, we also constantly have to make sure those laws, theories, and hypotheses still make sense. Sometimes, they might need a little tweaking, other times they need a major overhaul. Whatever changes are made, just know that scientific evidence is driving them.

Common Mistakes

Understanding theories, laws, and hypotheses can get confusing. Especially if you don't have Shmoop on your side. One of the biggest uh-oh's people make when it comes to understanding theories, laws, and hypotheses is thinking that they are hierarchical.

What we mean by that is that lots of people think that if we add more evidence, a hypothesis can become a theory, and a theory can graduate into a law. This isn't really the case, though. First of all, laws aren't the boss when it comes to scientific explanations. Scientists actually consider theories to be top dog when it comes to explaining stuff.

Secondly, we use laws, hypotheses, and theories to explain different things. For example, a law explains something specific, usually using a mathematical equation, and is supported by a lot of experiments and evidence. A hypothesis is an explanation for a specific phenomenon that can be tested by an experiment. A theory is an explanation, also supported by lots of experiments and evidence, for a broader concept or set of supported hypotheses.

Comparing these three is sort of like comparing a hippo, a huckleberry, and a housefly. The hippo isn't going to turn into a huckleberry, which certainly isn't going to turn into a housefly. At least not without us having to make some major changes to some pretty important theories.

Brain Snack

The Eridanus Supervoid is a giant (think 1 billion light years across) blotch in space that literally has no stars in it. There is a theory that it's a footprint left behind by a parallel universe. Just think, some student could be reading this exact same thing on a website called

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