The study of language development, the first intellectual achievement by a human being, has a long and rich history, extending over hundreds of years. The limitations of the behaviorist view of language acquisition, which heavily relies on imitation, reinforcement and correction, led in the 1960's to an alternative view arguing that human beings must be born with an innate capacity for language development. That is, the human brain is "ready" for language, in the sense that when children are exposed to speech, certain general principles for discovering and structuring language automatically begin to operate (Chomsky 1965 & 1981). As Chomsky argues, nativists or generative grammarians criticize the behaviorist view that language is a kind of verbal behavior which is "externalized" and exists independently of the mind. He maintains that language is governed by a set of highly abstract principles that provide parameters which are given particular settings in different languages (Ellis, 1997). Throughout this paper, arguments with supporting evidence will be presented to testify to the Chomyskian view of language, which is known as Universal Grammar.
The main argument which shows the psychological reality of language is the poverty of the stimulus. Chomsky realized the important role of input in language acquisition. There have been many questions about the possibility for children to learn the grammar of a natural language just by depending on the input they are exposed to. Some argue that if the grammar G of language L can be learned from the input alone, then Chomsky's claims about the genetic endowment of UG are false (Crain and Pietroski 1998). On the other hand, if young children know properties of grammar that are undetermined by the input, this proves that UG is operative and children do not have to learn the grammatical principles of UG. A much discussed example of the poverty of the stimulus is structure-dependent rules such as yes/no questions. Lasnik and Uriagereka (2002) discuss whether the knowledge of auxiliary fronting in yes/no questions can be inferred from the input if the child hears examples like:
Is the dog hungry?
Upon hearing question (a), the child will formulate hypothesis (1): "Front the first auxiliary" to make yes/no questions. However, when the child encounters a much more complex sentence:
The dog that is red is hungry.
He or she will apply hypothesis (1) to sentence (b), which consequently renders the sentence erratic:
*Is the dog that red is hungry?
Moreover, Lasnik and Uriagereka (2002) discuss different formulations that the child might consider such as (2) below:
a. Front the first auxiliary (that comes after an intonation change)
b. Front the first auxiliary (that comes after the first complete constituent)
c. Front the first auxiliary (that comes after the first semantic unit you parsed)
So a child without any previous knowledge of language applies all of the hypotheses in (2) mentioned above, he or she will not avoid an incorrect question such as:
*Are those who are coming and those who not coming will raise their hands?
The issue which is of paramount importance is why different children choose different formulations when they are faced with the task of making yes/no questions. If UG is not at work, then, children might end up learning "different grammars" because the hypothesis or generalization he formulates might be consistent with the primary linguistic data, but any attempt beyond such data will be linguistically inaccurate with the language spoken in the community (Lawrence and Margolis 2001). Therefore, UG, then, is "proposed as an explanation of how it is that language acquirers come to know, unconsciously, properties of grammar that go far beyond the input in various respects" (White 2003). White (2003) shows that such properties do not have to be learned; they are part of the "advance knowledge" that the child brings to bear on the task of acquiring a language.
Concerning the issues of collecting the kind of data that would support the UG, the particular question that faces any language acquisition researchers is how to discover our linguistic competence. Various methodologies have been developed over the years for investigating linguistic competence, and data have been obtained using different experimental techniques. It is, of course, the case that "no methodology allows one to tap linguistic competence directly: in all cases, performance factors will be involved" (White 2003). White (2003) mentions that the data collected to extract the UG can be classified into three categories: production data, including spontaneous and elicited production; comprehension data, including data obtained from act-out and picture-identification tasks; and intuitional data, including data from grammaticality judgments and truth-value judgments.
Grammaticality judgment (GJ) tasks are one of the most common data-collection methods that linguists use to testify to their theoretical claims. In these tasks, speakers of a language are presented with a set of linguistic stimuli to which they must respond. The elicited responses are usually in the form of assessments, wherein speakers determine whether and/or the extent to which a particular stimulus is "correct" in a given language. GJ tasks have some advantages in linguistic research because it shows how speakers react to types of sentences that rarely occur in spontaneous speech. Besides, it distinguishes distinguish production problems (e.g., slips, unfinished utterances, etc.) from grammatical production (Schütze, 1996). On the other hand, truth-value-judgment (TVG) tasks merely require the learner to indicate whether or not a particular sentence is true in a particular context. TVG tasks are designed to know whether children give more than one interpretation to certain sentences; for example, testing ambiguous sentences (Crain and Thornton 1998).
It is important to recognize that there is "no one methodology that is appropriate for investigating all aspects of linguistic competence" (White 2003). As far as the first language is concerned, the assumption is that language acquisition would be difficult if not impossible in the absence of innate capacity and specifically linguistic principles that exist in our minds. The major task that faces language researchers is to show appropriate techniques to tap this linguistic competence.