What Is a Litmus Test?

(Last Updated On: June 16, 2021)

When doing a simple gauge of how something is, you may have heard someone say they’re going to “take a litmus test” before. You might see this for politicians, where people will call a pulse-check on someone’s leading a litmus test. At least… that’s what the dictionary says about the political use of the litmus test. What even is a litmus test though? Where did we get them?

In Use

If you’re not familiar with the use of a litmus test as a social tool, let’s just go over that for a hot second. You do them all the time when you meet a new person. Ask someone if they’re a cat or dog person as a way to gauge their personality? Litmus test. Ask someone anything about their voting habits? Litmus test. Ask someone pretty much any question from this Reddit thread? Litmus test.

The point is, if you ask someone a question where the answer leads to some kind of generalization about their personality, you are performing a litmus test on them in real time. 

“Litmus test” being used as a metaphor in American politics is a pretty recent phenomenon (around the mid-20th century). Most commonly it’s used for nominations to the Supreme Court of the United States–politicians do a litmus test on nominees to see whether or not they will give the nominee their vote. With more recent relevance of single-issue voting, litmus tests in politics are also a good shorthand for determining who you would vote for. You probably have a list of things that, if a politician supported, they would immediately lose your vote–or gain it. 

Chemical Origins

Fortunately there is no chicken or the egg situation. The use of “litmus test” as a metaphor comes from its use in chemistry. Which means litmus is either named off of some old, dead scientist or it’s some important component to the chemical industry. Or it’s a chemical made by and named after an old dead guy. Lots of things in science are named after old scientists.

“Litmus” is derived from Old Norse for “moss” and “dye.” In Old Norse “mos” is moss and “litr” means to dye or stain. Mush them together and you get “litmose” and that later evolved into the litmus we’re familiar with. We also get litmus from lichens, which commonly include “moss” in their name–despite lichens not technically being mosses. Things like reindeer or Iceland moss may have moss in their names, but they’re technically lichens. Go figure.

Okay, so what the heck is litmus? Well it’s a mixture of dyes pulled out of lichens. There’s your name. Lichens aren’t moss, but they have moss in their name. Litmus is made from dyes, and there’s the other half of its original derivation. 

What’s it Used For?

If you’ve taken a middle or high school science class, you’ve probably done litmus tests! The chemistry one, not the one where you ask someone if they like puppies.

Litmus paper changes color when you put it in something that is acidic or basic, and it’s used to determine roughly how acidic or basic something is in terms of pH. You can read more about acids and bases here on the blog, but all you need to know for now is that pH is a unit of measurement of how acidic or basic something is. That’s why litmus paper has like 15 different dyes in it, they react to different pH levels. Stick it in some solution and the paper turns red? Well you know the solution is acidic now. If it turns blue, it’s basic. 

Speaking of moss, make sure you’re familiar with moss here.

About the Author:

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Kyler is a content writer at Sporcle living in Seattle, and is currently studying at the University of Washington School of Law. He's been writing for Sporcle since 2019; sometimes the blog is an excellent platform to answer random personal questions he has about the world. Most of his free time is spent drinking black coffee like water.