One of these shapes is called “bouba”.

The other is called  “kiki”. Which is which?

This was invented in 1929,  using slightly different words,

and it's been refined over time.

For most people, the  pointy shape is "kiki"

and the rounded shape is "bouba."

The majority of studies…

Wow, that is a lot of citations.

The majority of studies find that  pointy shapes are more associated with

unvoiced plosives and front  vowels: so “ta, pi, ka”,

and round shapes are associated with

voiced plosives, nasals, and  back vowels, so, “bou, gǝ, no”.

Okay, sure, but that's  just English, right?

We have words like  'point' and 'balloon',

maybe we're just copying the  associations from the words  

we already know.

One of the founders  of modern linguistics  

has an entire theory named after him,

about there being no  relation between the  

form of a word and what it represents.

But: there's a study  where English speakers

were given pairs of words  in a language from Peru.

In each pair,

one word was for a bird,  and one was for a fish.

And the English speakers,  who didn't know the language,

who knew nothing even  close to the language…

they could sort those  words into birds and fish  

a little bit better than chance.

Not well, but out of hundreds of people  answering thousands of questions,

they got 58% right. That is a  statistically significant result.

And there's another study where  Hebrew speakers were given pairs of  

Chinese characters with  opposite definitions,

and asked to match up the  characters and definitions.

Again, slightly better than  chance, about 55% right.

And if people who speak  different languages have even

a slight ability to figure out  completely unfamiliar words,

well, that raises the question,  

do humans have some sort  of built-in associations

between sounds and symbols  and things in the real world?

“Bouba” and “kiki” have been tested  in a lot of languages, and, yeah,

there seems to be something there,

what researchers call a type of  "crossmodal correspondence" or  

"sound symbolism."

Correlations between  phonemes, the sounds we make,

and traits like shape, texture,  brightness, size, or even taste.

Maybe that's down to cross-activation  between brain regions:

researchers into synaesthesia  have spent a long time on that.

Or it could be repeated association.

An elephant makes a  deeper sound than a mouse.

A large dog usually barks lower  and longer than a small dog.

If you shout into a big, round cave,

it'll reflect back deep,  round, resonating tones.

Shout into a tiny cave with  a lot of sharp angles in it

and you'll hear higher, sharper tones.

Something hard and brittle is more  likely to make a sharp 'kh' sound,

something like 'kiki', when you  hit it or break it or shatter it;

something soft and round is more  likely to make a noise like “bouba”.

I need to stress this is one  theory from a couple of papers,

don't take this as gospel, it's  right to be skeptical about that.

Plus, it doesn't always work.

A paper from 1975 shows the results of a  

bouba-kiki style test on Songe  speakers in Papua New Guinea,

where the results were like they were  picking at random. No preference.

And in 2017, another test on Syuba  speakers in Nepal, again: no preference.

The likely reason is that  the nonsense words they chose  

could not exist in those languages.

It'd be like giving English  speakers a test to choose between  

“ŋoba” and “tlet”.

You can't start a word  with ŋ or tl in English,

so the choice doesn't make sense.

The frustrating thing is: there  isn't much data on the failures.

Researchers often don't  publish their negative results,

and besides it's very difficult and  very expensive to give linguistic tests

to people who've never been exposed  to any of the major world languages.

But according to all those studies,

that bouba/kiki distinction  is true for most people.

There may be a link between some  sounds and some real-world properties.

And that may be why English  speakers were able to distinguish

birds and fish in that  Peruvian language:

the birds' names had more high,  front, non‐rounded vowels:

/i/ and /e/, they had  more “sharp sounds”.

And while there are  plenty of exceptions,

birds have more sharp beaks and  claws than your average fish does.