As mentioned in Section 3.1, the best model of grammar should be explanatorily adequate, which means that it should be able to account for all the data we observe, all of the grammaticality judgments we collect, and how the rules of grammar are acquired. Because of this, although Language Acquisition is an entire field of study on its own, morphologists and syntacticians also care about the language acquisition process.

Learning vs. acquisition

You may have noticed that we have said a lot about language “acquisition” but not about language “learning.” This is because, in linguistics, we distinguish between the two. When we say “acquisition,” we mean the development of something (in this case, language) subconsciously, by instinct. When we say “learning,” on the other hand, we mean that it developed consciously, through study and deliberate practice.

One piece of evidence that children acquire language, rather than learn it, is the course and timing of language development. Children typically acquire the majority of their grammar by the age of 4, before they go to school. This happens regardless of the language(s) they are exposed to. It also happens in different cultural contexts, in communities with vastly different traditions on how to interact with and speak to young children (see Figueroa in press and references therein). Children even begin learning the prosody of the language in their environment before they’re even born (Gervain 2013)! Children will usually not even repeat utterances that have grammatical structures that they have not yet acquired—to the point that asking children to repeat an experimenter’s utterance can be used in acquisition studies (for example, Kidd et al. 2006).

Compare that to the study of language in a classroom as a teenager or adult. In language classrooms, we often memorize and recite vocabulary and grammatical patterns. It takes effort and often makes your brain hurt! If you’ve ever studied a language as an adult or a teenager, think about how the process differed for you from acquiring a language as a child. If you’re like me, there were times that you could recite the verb conjugations for a test, but when it came time to use them in a real conversation, you couldn’t find the right form in your mind quick enough. This is what it feels like when you’ve learned the grammar consciously, but you haven’t acquired it subconsciously.

One of the puzzles of language acquisition is the fact that children do not seem to receive negative evidence. The majority of the utterances produced by the adults in their environment are grammatical. If the adults misspeak and produce an ungrammatical utterance, there is often nothing to indicate that they misspoke. It is difficult to identify even indirect ways children might get negative evidence. Some studies show that parents comprehend children’s ungrammatical utterances as frequently as their grammatical utterances, and that parents rarely correct children’s ungrammatical utterances, and instead respond to the content of their child’s speech (Brown and Hanlon 1970, as cited in Marcus 1993). When parents do correct their children’s grammar, it doesn’t usually work very well. Some famous examples include the following:

If we, as linguists, require negative evidence to figure out how grammar works, how can children manage without it?

Rule-based language learning

Let’s consider a toy version of English that contains three-word sentences consisting of a noun, a verb, and another noun. The toy version contains sentences like (1) that are sensible given the real world as well as sentences like (2) that aren’t, but that might be useful in fairy tale or science fiction contexts.

Again for the sake of argument, let’s assume a (small) vocabulary of 1,000 nouns and 100 verbs. This gives us a list of 1,000 x 100 x 1,000 (= 100 million) three-word sentences of the type in (1) and (2). Numbers of this magnitude are difficult to put in human perspective, so let’s estimate how long it would take a child to learn all the sentences on the list. Again, for the sake of argument, let’s assume that children can memorize sentences quickly, at a rate of one sentence a second. The entire list of three-word sentences could then be memorized in 100 million seconds, which comes to 3.17 years. So far, so good. However, the minute we start adding complexity to Toy English, the number of sentences and the time it would take to memorize them quickly mushrooms. For instance, adding only 10 adjectives to the child’s vocabulary would cause the number of five-word sentences of the form in (3) to grow to 10 billion (100 million x 10 x 10).

Even at the quick rate of one sentence per second that we’re assuming, the list of all such five-word sentences would take a bit over 317 years to learn. Clearly, this is an absurd consequence. For instance, how could our child ever come to know, as every English speaker plainly does, that the sentence in (4) is ungrammatical? If grammatical knowledge were based purely on rote memorization, the only way to determine this would be to compare (4) to all of the 10 billion five-word sentences and to find that it matches none of them.

And even after performing the comparison, our fictitious language learner still wouldn’t have the faintest clue as to why (4) is ungrammatical!

In addition to this thought experiment with its comically absurd consequences, there is another reason to think that language acquisition isn’t entirely based on rote memorization – namely, that children use what they hear of language as raw material to construct linguistic rules. How do we know this? We know because children sometimes produce rule-based forms that they have never heard before.

One of the earliest demonstrations that children acquire linguistic rules, rather than simply imitating the forms of adult language, was the well-known wug test (Berko 1958). In it, the psycholinguist Jean Berko used invented words to examine (among other things) how children between the ages of 4 and 7 form plurals in English. She showed the children cards with simple line drawings of objects and animals and elicited plurals from them by reading them accompanying texts like (5).

More than 75% of the children pluralized the invented words cra, lun, tor, and wug in exactly the same way that adults did in a control group: they added the sound -z to the word (Berko 1958: 159-162). Since none of the children had encountered the invented words before the experiment, their response clearly indicates that they had acquired a plural rule and were using it to produce the novel forms.

Children are also observed to produce novel rule-based forms instead of existing irregular adult forms (for instance, comed or goed instead of came or went). This process, which is known as overregularization, is further illustrated in (6) (Marcus et al. 1992: 148-149, based on Brown 1973).

Overregularized forms don’t amount to a large fraction of the forms that children produce overall (less than 5% in the case of past tense forms, according to Marcus et al. 1992: 35), but they are important because they clearly show that even the acquisition of words can’t be completely reduced to rote memorization.

Check yourself!

References and further resources

Attribution

Portions of this section are adapted from the following CC BY NC source:

↪️ Santorini, Beatrice, and Anthony Kroch. 2007. The syntax of natural language: An online introduction. https://www.ling.upenn.edu/~beatrice/syntax-textbook

Comedy and satirical linguistics

🎉 Dresher, B. Elan. 2010. The Geese Rethink Innateness. Toronto Working Papers in Linguistics 32. https://twpl.library.utoronto.ca/index.php/twpl/article/view/13954

For a general audience

🧠 CrashCourse. 2020. Language Acquisition: Crash Course Linguistics #12. https://www.youtube.com/watch?v=Ccsf0yX7ECg

🧠 NOVA PBS Official. 2010. The secret life of scientists and engineers: Jean Berko Gleason and wugs. https://www.youtube.com/watch?v=ElabA5YICsA

Academic sources

Berko, Jean. 1958. The child’s learning of English morphology. Word 14: 150–177.

Brown, Roger. 1973. A first language: The early stages. Cambridge, MA: Harvard University Press.

Braine, Martin D. 1971. On two types of models of the internalization of grammars. In Dan Slobin (ed.), The ontogenesis of grammar. New York: Academic Press. 153–186.

Brown, Roger & Camille Hanlon. 1970. Derivational complexity and order of acquisition in child speech. In John R. Hayes (ed.), Cognition and the development of language. New York: Wiley. 11–53.

Chomsky, Noam. 1959. Review of Verbal behaviour by B.F. Skinner. Language 35(1): 26–58.

Figueroa, Megan. (to appear). Language Development, Linguistic Input, and Linguistic Racism. WIREs Cognitive Science.

Gervain, Judit. 2018. The role of prenatal experience in language development. Current Opinion in Behavioral Sciences 21: 62–67.

Kidd, Evan, Elena Lieven, & Michael Tomasello. 2006. Examining the role of lexical frequency in the acquisition and processing of sentential complements. Cognitive Development 21(2): 93–107.

Marcus, Gary, Steven Pinker, Michael Ullman, Michelle Hollander, T. John Rosen, and Fei Xu. 1992. Overregularization in language acquisition. Monographs of the Society for Research in Child Development 57(4). Chicago: University of Chicago Press.

Marcus, Gary F. 1993. Negative evidence in language acquisition. Cognition 46(1): 53–85.

McNeil, David. 1966. Developmental Psycholinguistics. In Frank Smith and George A. Miller (eds.), The Genesis of Language: A Psycholinguistic Approach. Cambridge: MIT Press. 15–84.

Skinner, B.F. 1957. Verbal behaviour. New York-London: Appleton-Century.