That no culture in the world has been discovered where human beings do not communicate in spoken language can be seen at the individual level by the rapidity and competence with which children assimilate and use a vast vocabulary by applying complex grammatical rules to express highly abstract thoughts. That language may be the dynamo which elevates man above his genetic cousins has also been considered, made possible by its infinitely generative nature.
The three aspects of language acquisition are:
1. phonology � speech sounds
2. semantics � meanings of words
3. syntax � assembling the words in order using the rules of grammar
A complete sentence can be broken down at various levels, including:
1. phonemes � the smallest unit of sound to affect meaning
2. morphemes � units of meaning (stems and affixes, which include prefixes, suffixes and infixes)
3. words
4. phrases � meaningful groupings
5. sentences
A child�s first words are produced at around 12 months. After this, the first words children tend to learn are verbs. Harris et al noticed a very strong (+0.94) correlation between naming and pointing at objects (noun development), and to a far lesser extent, between poiting and other aspects of language development up until the vocabulary spurt.
In line with noun learning, certain non-nominal expressions are used frequently, words such as �no�, �more� and compounds such as �allgone�. These seem to play an important role in language acquisition, and Gopnik and Meltzoff links them with related cognitive development.
After about a year and a half, the vocabulary spurt begins during which children�s ability to learn and comprehend words rises astronomically, both of which Reznick and Goldfield have seen in a longtitudinal study to occur at about the same time.
By the age of about 6, children have learnt over 15,000 words, equivalent to an average of about one word per waking hour. Carey described this process as �fast-mapping�, demonstrating that 4 and 5 year olds when presented with a new word (the colour �chromium�) in the context of a sentence would be able to pick out the chromium tray from eight others a week later.
After almost two years, children start to combine words, usually in pairs, such as �Adam fall� and �allgone ball� to describe events and actions. Brown also tracked a sequential development of the use of morphemes during the third year, such as inflectional affixes.
By the fourth year, infants are able to employ auxiliaries and their negatives, the future tense and questions. Slobin and Bever showed that 3-4 year olds cannot yet enact passive sentences (especially those without an overt action), whose findings have been confirmed by Kerstin Meints who showed that children do not produce passive sentences when questioned about what happened to the recipient of an action.
Marcus et al�s studies on over-regularisation (applying regularisation rules such as �run-ran� in the past tense to �bring� to get �brung�) indicate a conflict in the sequence of their semantic and syntactic developments, as they initially learn the correct form, then learn the regularisation rule and then apply it too widely.
Chomsky noticed further small difficulties children have, such as discriminating sentences with similar surface structures (as opposed to the �deep� or underlying structure which is what we translate into in our minds, �mentalese�), e.g. �X promised Y to do something� as opposed to �X forced Y to do something�. He points out that without an ability to break sentences down structurally into phrases, whose constituents may not even be contiguous, many inversions, interrogations and embedded relative clause constructions would be impossible to use.
Chomsky�s ideas are part of his attempt to explain how infants acquire syntax (for which he argues the need for an innate mechanism, as does Pinker). The evidence for this is varied and interesting, including: the almost inevitability of a child learning a spoken language given even minimum stimulation, as opposed to the difficulties of learning to read; the impossibility of learning to comprehend, let alone speak a discrete combinatorial infinitely generative language; the degree of abstract learning necessary, requiring structure-dependent learning; the unsystematic syntactic correction they receive from parents; the evidence (Brown, Fromkin) of children deprived until a late of age of speech input who still learn to talk to a greater or lesser degree (including tribes where ignoring children of a young age is the custom); and the ease with which pre-pubescent children pick up second languages.
However, even Fernald and Akhtar et al.�s studies which aim to demonstrate the primary importance of experience over innate mechanisms stress the motherese argument and social interaction and novelty. Mothers in various cultures use this exaggerated, slowed and simplified form of speech to their children which is believed to hold the infant�s attention and thus aid their learning more than the rapid and muted tones of adult conversational speech.
Experiments with other higher primates using animal sign language (ASL), which can comprise of hundreds of �words�, are beginning to demonstrate that it might be the combination of our phonological, semantic and syntactic aspects of language which make it so versatile and, as far as we know, specific to man at this level.