What are typical vocabulary growth rates (say, in words / day) for children and adults in their native languages? Has there been enough research to plot vocabulary growth rate vs age?

I'm especially interested in how many new words adults learn per year, on average, simply due to new words entering the language.

I'd guess adults probably still learn words at a surprising rate due to the evolving language, but also that kids still beat them out of the water. But it would be nice to quantify this.

  • No, there is not anywhere near enough research for this. To start with, not all languages have what you think of as "words", so they can't be compared and counted easily. There is data on specific individuals, but nothing that would allow generalizations.
    – jlawler
    May 23, 2019 at 16:12
  • Even just data within one language would interest me. At least for babies learning language X versus native-speaker adults learning new words as language X evolves, whatever we consider "words" in language X would be consistent for both.
    – WillG
    May 23, 2019 at 16:16
  • There usually isn't any "versus". There was recently a grad student somewhere (MIT?) who recorded every minute of their son's experience in sound video for the first two (maybe three?) years. So it's known what language went in and what language came out. That's not the same as learning rates, though, even if you do the arithmetic; learning to understand is vastly different from learning to produce.
    – jlawler
    May 23, 2019 at 16:29
  • I totally get that it's arbitrary and difficult to decide what counts as a word, what counts as "knowing" a word, and how to measure that knowledge. But I thought that's what linguistic researchers were good at and have been doing for a few decades.
    – WillG
    May 23, 2019 at 16:38
  • Some linguistic researchers have been doing things like that. But we're not in charge of the educational system, you know, and English and language learning (both first- and second-language varieties) usually don't follow what linguistic researchers have found. And they consistently mix up writing and reading, which are not natural, with speaking and understanding, which humans are evolved to do.
    – jlawler
    May 24, 2019 at 1:10


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