The human language is characterised by the following things:

1. Communication system
   It is a communication system, a means for speakers of a language to communicate with one another. This part is not unique to human language.
2. A symbolic system
   It is a symbolic system because words and parts of words represent meaning. They refer to something other than themselves. Language systems are arbitrary.
3. Rule-governed system
   It is a rule-governed system. Each human language is constrained by a set of rules that reflect the regularities of the language.
4. Productivity
   It is productive because a finite number of linguistic units and a finite number of rules are capable of yielding an infinite number of grammatical utterances. Speakers are not restricted to reproducing sentences they have already heard.

Language consists of several systems, the pragmatic system, the phonological system, the syntactic system and the semantic system.

The pragmatic system refers to the abilities that enable us to communicate effectively and appropriately in a social context. It involves a variety of cognitive and social skills. Turn-taking is important in language because the speaker needs to become the listener and vice-versa after a while. Turn-taking is already present in infants, as is shown by proto-conversations, interactions between adults and infants in which the adults tend to vocalise when the infants are not vocalising or when the infant has finished vocalising. Proto-imperative occurs when infants point to an object and then alternate their gaze between the object and the adult until they obtain the desired object. Proto-declarative occurs when infants use pointing or looking to direct an adult’s attention towards an object. The pragmatic system consists of several parts:

1. Imitation
   Infants are able to imitate and imitation in various play activities is an important precursor to the development of language, especially the pragmatic system.
2. Initiating interactions
   The first attempts to initiate interactions are non-verbal. Pointing plays a big role in non-verbal interactions. As children acquire language, initiating interactions becomes less gestural and more verbal.
3. Maintaining conversations
   Children must learn to add relevant information to the dialogue as well as learn when it is their turn to speak.
4. Repairing faulty conversations
   Children must learn when and how to repair conversations as miscommunications occur. In order to do this, the child must understand that a miscommunication has occurred and understand how to correct the problem. Adults play a big role in this part.

Phonology is the aspect of language about the perception and production of sounds that are used in language. In order for effective communication to occur, children must learn which sounds are important in the language that they hear.

Children must learn to separate the speech stream into individual sounds and sound combinations. This is facilitated by infant-directed speech. Children prefer to listen to human speech than other environmental sounds. Adult speakers can discriminate between sounds that differ in a category, but can rarely discriminate between sounds in the same category. Infants are able to discriminate between phonemes. Even young infants engage in the categorical perception of speech sounds. Categorical perception may be an innate mechanism for interpreting sounds. The ability to discriminate possible phonemes diminishes with age. Children’s acquisition of the phonemes of their native language depends on both the innate predisposition for categorical perception of sounds and experience with sounds used as phonemes in their native language.

All children pass through the same phase of vocal production, which consists of the following phases:

1. Reflexive vocalisations (birth – 2 months)
   Reflexive vocalisations are cries, burps, coughs and sneezes. The type of cries changes according to the situation. The characteristics of cries change in response to the experience of various emotions and contexts.
2. Cooing and laughing (2 – 4 months)
   Infants begin to laugh and to combine sounds with one another. The reciprocal cooing between infant and parent may help the infant to learn that communication involves taking turns.
3. Babbling and vocal play (4 – 6 months)
   Babbling is the play with sounds. It is a type of controlled vocalisation. Infants begin to produce a wide range of sounds and sound combinations.
4. Canonical babbling (6 – 10 months)
   Infants begin to produce sound combinations that sound like words, but the infants do not attach meaning to these sound combinations yet. Hearing human speech or having others respond to infant vocalisations are not necessary for early babbling to occur. Manual babbling is the sign-language equivalent of babbling. Interaction is important for the continuation of babbling and language development.
5. Modulated babbling (10 months on)
   This period is characterised by a variety of sound combinations, stress and intonation patterns. This period overlaps with the beginning of meaningful speech. It may play an important role in the acquisition of the intonation patterns that are important for the infant’s native language.

Children are more likely to use words that they can pronounce correctly. This suggests that they are aware of the differences between their incorrect pronunciations and the correct ones. As children learn to produce correct pronunciations, they may produce phonological distinctions that adults cannot perceive.

Syntax deals with the manner in which words and parts of words are related to one another to produce grammatical sentences. Chomsky has suggested that the syntactic structure of every human language is the result of an interrelated set of elements. The s-structure (surface structure) corresponds to the spoken language and the d-structure (deep structure) is a more abstract representation of a sentence.

Between 10 and 18 months children begin to produce single word utterances. Children comprehend more than they can produce. Between 18 and 24 months, children begin to produce two-word utterances. Children are the most likely to use words that are highly salient in their environment. Children may be primed to learn patterns or rules and novel words early on. It is unknown how much children know during the two-word period or how they know it. After the two-word period, syntactic knowledge increases rapidly.

Overregularization refers to when a previously learned rule is applied in the wrong situation. The errors children make demonstrate that they are learning the syntactic rules. Children regularly make mistakes in plurals, past tense and they make creative overgeneralisation (e.g: using -ing after nouns, thus creating a new verb). An overgeneralisation is creating a new verb by treating a noun as if it were a verb.

Chomsky stated that children are born with innate knowledge of language. Language requires the ability to relate d-structures to s-structures. The environment only provides children with information about s-structures, so they have some knowledge about d-structures. The sentences that children hear are complex and often ungrammatical. Children receive little feedback about the grammatical correctness of their utterances and children acquire their first language relatively quickly and easily and this leads to the conclusion that children have innate knowledge of syntactic structures.

Parents barely correct their child’s wrong grammatical utterances and sometimes even reinforce it. When the child is corrected, it may leave the child confused. Chomsky claims that parents do not play a significant role in children’s syntactic development. Children hear a more simplified version of language.

In order to learn a word, children must hear it being used. Infants learn some of the words in their environment. The manner in which a child interprets a recently discovered word depends on the child’s existing semantic system, their knowledge of the world, the level of their cognitive skill and selective attention. The child who extends the meaning of a word too broadly is making an overextension error.  An underextension error, extending the meaning of a word to too few instances, is also possible. Children make few of these mistakes.

There are several possible constraints to influence word meaning development, including the following two:

1. Whole object constraint
   This assumes that children believe that words refer to whole objects rather than to parts of objects.
2. Mutual exclusivity constraint
   This assumes that children believe that there is a one-to-one correspondence between words and meanings.

A semantic system is a system that categorises words in relation to their meaning. The development of the semantic system is facilitated by children’s acquisition of semantic relations. Words that fall in the far ends of the dimension (e.g: hot and cold) are learned before words that fall between the two extremes.

Before children begin to acquire words, they have formed concepts of the world. Children’s first words are most likely to be those that express these early concepts. Hearing a novel word causes children to search for the meaning of the word, which often results in new concepts being learned. Children use two strategies when faced with gaps in their semantic and/or conceptual system:

1. Acquiring a new word
   Known concepts are searched in case the word denotes a previously acquired concept. If no existing concept seems appropriate, construct a new one.
2. Acquiring a new concept
   Attempt to attach a known word to it. If no existing word seems appropriate, look for one.