If you’ve ever heard someone speaking in a language other than your own, it might have sounded like they were talking five times faster than you ever have. Or perhaps their language was slow and deliberate, maybe even poetic. Does that mean that “speedy” language speakers are more efficient at communicating more information in less time? Not necessarily.
In fact, one study tracked the information transmitted in 17 languages. They discovered that it’s actually the brain itself that determines how much information language carries, with languages converging on roughly the same information rate regardless of speed. This balance points to a universal ceiling set by the brain, not the mouth: about 39 bits per second.
Understanding the “Speed” of Language
To examine how fast a language moves, it’s more useful to analyze the speed at which information is conveyed rather than how frequently sounds appear. This provides the best glimpse at whether fast talkers are actually “communicating” faster. To this end, scientists measure information transfer in “bits.”
Bits can be described as information-theoretic units. In other words, they are not individual thoughts or facts. They are a measure of predictable context, where more information is gained when the listener eliminates uncertainty. Consider, for example:
She spread the butter on the ____.
You probably thought of bread. Because it’s predictable, it’s not “worth” very many bits. However, if she spread butter on the radiator, you probably couldn’t have predicted that. Such highly unexpected information eliminates significantly more uncertainty once you hear it, so it’s ascribed a higher value in bits.
Which Languages Are the Fastest and the Slowest?
When scientists attempt to determine which languages are fast or slow, they run into a surprising fact: they’re actually all about the same. Fast languages tend to produce more syllables, but each of those syllables contains a lower average bit density. Conversely, a slower language tends to pack more bits into each syllable. Thus, they converge around approximately 39 bits per second.
Languages are predisposed to being regarded as fast or slow based on their construction. Japanese, for example, operates in simple and consistent syllable-like units, almost exclusively in consonant-vowel sequences. Because each unit distinguishes among fewer possible forms, speakers need to hear more units in order to parse a message. Thus, Japanese seems to flow quickly but without carrying more information.
Information Density and the Limitations of the Brain
Why 39 bits per second? The human mouth can speak quickly, after all. Could we not learn to talk faster and convey more information? Language production has developed over time in tandem with the constraints of the brain. Human listeners can only process so much information at once, and speech requires the brain to perform multiple simultaneous tasks: identifying sounds, predicting upcoming material, understanding syntax, working through meaning, and revising interpretations, all while the sentence is still being revealed.
Over time, societies have found that happy medium of 39 bits per second, which is high enough to count as efficient but low enough that understanding comes easily. In some niche scenarios (e.g., air traffic controllers), you may encounter speech well in excess of 39 bits per second. These professionals communicate at speed in highly industry-specific terms that may be nigh-unintelligible to outsiders. The standard of approximately 39 bits is why these situations seem extraordinary to the average listener.
However, it is important to remember that studies on language speed point to a pattern, not a hard and fast rule. The 17 languages included in the comparison functioned similarly, but they are just a small fraction of the languages found around the world. In the study, the speakers read pre-selected passages, which are different from spontaneous conversation where a person might pause, correct themselves, interrupt, emphasize, or be operating on shared context with the listener. Thus, it is not entirely true to say that every language has the same “speed limit.” Rather, languages tend to converge around the same operating range, with some tradeoffs and divergences among them.
The next time you speak, try talking as fast as you can. You might find that if your mouth doesn’t fail you first, your mind might struggle to put everything together ahead of your words. This is just one representation of a person’s mental capacity expressed in bits.
