Spoken communication requires human beings to be able to do two separate things:

The first is to understand what is being said to them (including isolating the sound of the other person's voice from all the other noises in the environment, resolving the sound to a set of words and pauses, and processing the words and pauses to extract meaning from them). The second is to communicate their own ideas to the other person (by formulating them into a sequence of words and pauses, and speaking these aloud in such a way that the other person can extract meaning from them).

Now, we are for the most part only able to do one of these things at a time (and often with a small pause in-between while we process what has been said to us and decide what we want to say in return). I'm wondering, if this wasn't the case, and both tasks could be done simultaneously without interfering with each other, would language have still developed in the way that it has? Would grammar still operate in the way that it does?

If not, what differences might we expect to see?

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    $\begingroup$ We already are able to do that. The main reason we're not talking and listening at the same time is that what we say has to be based on what we hear. $\endgroup$
    – Annonymus
    Dec 4, 2016 at 17:52
  • $\begingroup$ FSK (Frequency Shift Keying), TDMA (Time Division Multiple Access)... many other well documented and interesting telecommunications technologies. $\endgroup$
    – Wossname
    Dec 4, 2016 at 17:54
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    $\begingroup$ I’ve heard that people in high-pressure, time-critical jobs with information overload (e.g., pilots and air traffic controllers) develop the ability to absorb multiple data streams — specifically, multiple audio (voice) streams — simultaneously.  I expect that the best emergency services (‘‘911’’) dispatchers do exactly what you’re talking about — notify the police, fire department, and/or paramedics while listening to the caller.  (Granted, this may be done digitally rather than vocally, but I’m not sure that makes a difference.) $\endgroup$ Dec 4, 2016 at 21:22
  • $\begingroup$ I +1'd this because I think its a great question, but I wish I could +1 it again for instigating all these good answers. My answer is competing with good company! Great first question, TheTermiteSociety, and welcome to WorldBuilding! $\endgroup$
    – Cort Ammon
    Dec 5, 2016 at 4:37
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    $\begingroup$ Another example of people that listen and talk at the same time: Simultaneous translators. $\endgroup$ Dec 5, 2016 at 10:35

4 Answers 4


This is interesting to me because what you want to explore both happens and doesn't happen. As you have noticed, it's mighty difficult to hold a conversation when both parties are trying to talk over each other. However, we have plenty of examples in singing where we indeed are vocalizing over the top of someone while listening to them. There's no other way a barbershop quartet could maintain the locked down harmonies they need to sound as they do.

This points to something deeper in our psyche. Something about the way we think about communication causes us to choose not to speak in the way you describe. That makes it fun because this also suggests that this inability to speak and listen may be cultural, not biological. Cultural things are always fun to dig into, but first, some biology.

One key limitation with any human cognition is how slowly the brain processes novel stimuli. If it's prepared for a stimulus, the brain can respond within 106ms (that time was achieved by an Olympic athlete in a carefully structured test). However, if the brain is less prepared, it's slower. There's a pair of brainwaves scientists love to use in psychological experiments called P300a and P300b. Each of these occurs at roughly 300ms after a novel stimulus (hence P300). P300a is in response to an unexpected stimulus (such as a loud noise), while P300b is in response to an unexpected stimulus that is related to the current task at hand (such as a the stoplight turning yellow while you are driving). Scientists love these because they are very easy to distinguish, and are well correlated to cognition itself.

This shows a lower bound for communication "at the same time." If your stimulus needs to reach my upper cognitive functions, they don't even start processing until 300ms after you've made your sound and you'll probably need a few hundred milliseconds to process it. Most conversations are held at 110-150wpm (400-545ms per word), and while I don't have any scientific evidence to back it up... this sure looks like those two timelines are strongly related.

Another limit is that upper cognitive functions tend to be more serial and less parallel. Its a lot harder to be counting backwards from 100 by 7's while listening to someone speak than it is to do one or the other. This naturally serializes the conversation.

However, I did mention that we do listen while we speak, and gave singing as an example. Staying in tune is a lower cognitive function, in that singers aren't actively thinking about it most of the time. We singers tend to learn to automatically stay in tune. This means we don't need to have any of those slow P300 waves firing to stay in tune. We can use the lower and faster functions of the brain to communicate.

So what if we used those lower parts more when we communicated? I think there's a lot of room for interpretation there, because that part of the brain is not very well understood. We don't quite know what it would look like if it was communicating more directly than it does. However, we have a few examples of what it might be. There's a particular example that comes to mind, the Kecak style performances from Bali, Indonesia. It is believed to have its origins in an exorcism ritual. I will be the first to admit that, as a white US citizen, I don't fully understand what is going on here, but when I think about what it would look like for us to drop the walls we put up around our brain and let the lower functions communicate with one anothers', I get the impression it might look something like this. I don't know about you, but I get an eerie feeling when watching their dances, like they're reaching out to me in a way I don't fully comprehend. Maybe there's more to this than meets the eye.

  • $\begingroup$ There are some fascinating ideas in this answer (thank you). I think there's probably some significance to the distinction between doing this for what you call "higher" (which I'm interpreting as complex and conscious) thought, and what you call "lower" (which I'm thinking of as subconscious or simple) thought. I could imagine a language which allows for the speakers to pretty-much constantly communicate their feelings and most intuitively held beliefs about something (simultaneously), while still requiring them to turn-take for more demanding communication. $\endgroup$ Dec 5, 2016 at 8:36
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    $\begingroup$ @TheTermiteSociety and that is called mimics and cues. We do it all the time, while speaking we read the facial expression of the listener and adapt to his feelings, while also communicating our own with our face and hands. We are speaking and listening at the same time, just not with words - words are for high-level concepts. $\endgroup$
    – Falco
    Dec 5, 2016 at 10:02

Cort Ammon's answer is good, but I want to add comments and I have more commentary than the comment section will take.

Human language has the flexibility for simultaneous conversation

First, as he pointed out, the human language is very flexible. There are so many things that you can do with your voice above and beyond what we use to speak. For example, English speakers do not use tone like the Chinese do (while the Chinese don't use grammatical tense). There are at least 150 unique phonemes (sounds, roughly) that are used in speech by various human groups. !Xuun uses something like 141 of them; English uses up to 47 (21 vowels, 26 consonants, although not all dialects pronounce all sounds).

The point is, by using different sounds or tones two people could talk at the same time and be perfectly intelligible by not sharing similar sounds that would interfere with each other. A language could theoretically develop where there was a '1st speaker' and '2nd speaker' using different sounds and tones, so that two people could use one of the two speaker dialects to talk at the same time. '1st speaker' could use all short vowels and '2nd speaker' could use all long vowels for instance. Or it could be so easy in a tonal language like Chinese that the second speaker raises or lowers his voice a major fifth away from the first speaker, so their speech doesn't overlap on tones.

Regardless of the above, the human ear and brain is sufficient to track multiple conversations at once. It is hard to 'comprehend' two conversations at once, as we'll discuss next, but most people have picked out their own name in a converstion across the room. Further, anyone with kids can tell you that you can hear what your kids are saying even if you are talking to someone else.

The human brain is not set up for simultaneous conversation

Again, following Cort Ammon, our brains are not set up to process language at the same time as we speak it. Just try it, it is very hard to order your thoughts while you are listening, or even if you are reading.

It is interesting that expressive and receptive aphasia (inability to speak language, and comprehend language, respectively) are tied to different areas of the brain. So it is not that easy to assert that there is some shared hardward that is used for both expressing and recieving language that prevents us from doing both at the same time. But the proof is simply in testing it yourself. Try to read a sentance from this answer while reciting something you have memorized, then try to repeat what you just read. You just can't do it (at least I can't).


The human language is flexible enough to support simultaneously speaking and listening, but the brain just isn't up to it.

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    $\begingroup$ "our brains are not set up to process language at the same time as we speak it" - this is just not true. Our brain can even more! Think of simultaneous interpretation, that requires listening and speaking in two different languages! $\endgroup$
    – vojta
    Dec 5, 2016 at 7:46
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    $\begingroup$ @vojta I'll admit, I hadn't thought about real-time translation. Is it possible the fact that they're using two different languages actually makes it easier, though? Maybe not, but if so, that could have huge significance for any language that developed for simultaneous communication. $\endgroup$ Dec 5, 2016 at 8:28
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    $\begingroup$ @vojta Good point, though I'd argue that real-time translation falls under a different case, since you are listening and repeating the same concepts; which I (not the slightest authority in the matter, to be honest) consider a different case from dealing simultaneously with different concepts, like a conversation or the aforementioned example Try to read a sentance from this answer while reciting something you have memorized, then try to repeat what you just read. $\endgroup$
    – xDaizu
    Dec 5, 2016 at 12:32
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    $\begingroup$ @xDaizu I would argue that real-time translation is way harder than it seems. Languages frequently don't match 1:1 regarding concepts, and often you are more interpreting what is said than really translating it. As an example, Portuguese has way more words than English. If you try to real-time English-to-Portuguese speech, you would have to translate huge chunks of word at once just to understand which nuances you need to convey in Portuguese. Just check how many words there are for translating something like "over" to Portuguese - it has over 20 direct translations possible. $\endgroup$
    – Mermaker
    Dec 5, 2016 at 13:35
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    $\begingroup$ @vojta You did not read carefully what I am saying. When you are simultaneously interpreting, there is only one train of thought. The language comes in, gets interpreted into a set of thought patterns, then the same thought patterns go out in a different language. A conversation requires you simultaneously process what is coming in, and develop a response. That is two different trains of thought. That is the part that is not possible. $\endgroup$
    – kingledion
    Dec 5, 2016 at 13:50

There's a real-life example of listening and speaking at the same time in the case of real-time translators. This is at a different time-scale than milliseconds; a translator typically needs to hear a few seconds of speech before they begin translating, and depending on the languages involved or if ambiguities arise may want to build up a longer backlog of speech. Note that although they are delaying their responses to initial stimulus by several seconds, they are speaking at the same time they are listening to the sentences they are going to translate a few seconds later.

If nothing else, it's proof that humans are capable of tasks like this; the rarity of it demonstrates more that it is not generally useful than that it is impossible. The reason it's not useful is elaborated on in other answers: most communication is serial, and we must hear the end of a question in order to answer it (unless we guess the end of the question correctly; but this is still a serial communication, because we at least need to hear the important parts before we answer).

Being able to speak and listen at the same time would only be useful for non-serial communication, and I'm not sure what the advantage of such communication would be. A group of people relaying status updates simultaneously might qualify, or holding two separate conversations at the same time. The latter happens often when there is a delay in responding, for instance in letters, emails, or chat rooms; it is not inconceivable that it could happen for spoken conversations, as you often know completely what you want to say before you finish saying it, which frees up your mind for listening to something else and formulating a reply to that, too. Again, it seems of limited benefit unless you have an interview with a lot of questions and not enough time to ask them all.

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    $\begingroup$ Translators boggle my mind. If we couldn't witness them doing it every day, I'd say what they do is impossible! $\endgroup$
    – Cort Ammon
    Dec 5, 2016 at 4:35
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    $\begingroup$ I wonder to what depth translators experience what they are translating, for example, if translating a TED talk, do they walk away with a deeper understanding than the average audience member since they carefully process each and every word spoken, or do they need to watch a recording later to understand the higher concepts since they were so focused on the translations? $\endgroup$
    – Phlarx
    Dec 5, 2016 at 16:17
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    $\begingroup$ I've read that another real-life example is sign language between 2 people (doesn't work in larger groups, of course). $\endgroup$
    – npostavs
    Dec 5, 2016 at 17:04

There is a reasonable case that this is exactly what does happen. Quite a lot of human verbal communication is a bit redundant purely in terms of the information content and in many cases the real conversation is more about more subtle cues of tone, context, inflection and body language and quite a lot of conversation is more or less automatic in terms of the mechanics of grammar and vocabulary.

Most of the time in casual conversation we are able to formulate concepts and inflect quite subtle nuances without really thinking much about it. Just thing about the difference in he way you talk to a good friend, a casual acquaintance, your boss, someone you are attracted to etc etc.

I saw a good example only today in the form of a theatrical audition workshop where people were asked to tell a story and were occasionally stopped and given new and unexpected context. For example mid sentence they might be stopped and asked to imaging that they were telling the same story but they were in a job interview or giving a speech at a wedding or trying to scare someone around a campfire. You could immediately see the proficient actors, not because they were able to make up new lines on the spot but because they were able to put themselves into that context and their whole delivery changed in a way that you might not notice in a written script.

They key point here is that a lot of the mechanics of language is entirely separate from conscious, rational thought and thinking about what you are going to say next while the other person is still speaking is an entirely normal part of conversation.

Indeed there is an argument that in a modern context where we have to deal with very complex concepts and technical information that we were never evolved for there is actually too much parallel speaking and listening and we would be better off with a language convention which didn't rely so much on a more or less instantaneous response.

Consider also that in most casual social contexts pauses in conversations are often considered as awkward (and acceptable pauses have been measures as being very small indeed) , this in itself implies that we are well able to start formulating a response long before the other person has finished speaking.

In some ways literature sums this up better than science and it would be worth looking at writers like Pratchett, Pinter, Austin and Wodehouse to get a sens of just how flexible and nuanced dialog can be.

  • $\begingroup$ I think you're right about subtle nuances, and that we already do this to some extent. We certainly do tend to throw in a fair amount of 'yeah's and 'hmm's and 'ah, alright's when we speak to people we're familiar (or otherwise comfortable) with. Is it really true that we cram as much information as possible into these responses, though? Do we unambiguously distinguish in this way between "I completely agree and I'm delighted about it", "I think I agree, but I have to think about it more", "I agree, but I'm not pleased about it" etc.? Maybe the reasons we don't are cultural, though. $\endgroup$ Dec 5, 2016 at 8:47
  • $\begingroup$ You already do - if you talk about how cool trains are and your friend is rolling her eyes while you do. You will adapt your speech to this new information you got simultaneously to talking. $\endgroup$
    – Falco
    Dec 5, 2016 at 10:04
  • $\begingroup$ @Falco Ok, it's totally my fault here for choosing bad examples (since each, as you rightly say, can be expressed through body-language), but that isn't quite what I meant. I'm not neglecting body language or the paralinguistic features of speech. Rather, I'm wondering how much extra information of this sort could be incorporated into spoken language to supplement it, and I'm noting that we already do this in a small way with our noises (words) of agreement, disagreement, approval, disaproval, etc. (suggesting to me that these things don't necessarily have to be non-verbal). $\endgroup$ Dec 5, 2016 at 11:23

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