In addition it must have all the other information about the word’s meaning, morphology and pronunciation.

So, as well as principles and parameters knowledge of language means knowing vocabulary. All verbs, and in fact all lexical items, are used in sentences according to a set of complex specifications.

Knowing the grammar of a language is no use without also knowing how each word behaves in the sentence.

The structure of a sentence is an interplay between its structure, as laid down by the principles and parameters, and the individual properties of the lexical items. Learning the universal principles may not require much effort, since these are automatically imposed by our minds. Setting the values of parameters may also be straightforward, since these take only a few sentences to observe. The task of learning the idiosyncratic behaviour of thousands of words is, however, difficult. So, overall knowledge of language comes down to a combination of principles, parameters and vocabulary. Since the principles are already specified, knowledge of a particular language amounts to knowing the vocabulary and the parameter settings.

As far as the vocabulary is concerned, everything that is learnt is part of the lexicon which is part of human knowledge of a language where words and the information about their use are stored. But, if all learning is vocabulary, parameters must also be part of the lexicon. An illustration of this comes from the binding principles. These state that in the sentence Helen said Sarah respects herself the reflexive pronoun herself is bound to Sarah and so refers to the same person.

H elen said Sarah respects herself

However, in Helen said Sarah respects her the pronoun her may not be bound to Sarah, and so refers to someone else, whether to Helen or to a person who otherwise is not mentioned. (someone else)

H elen said Sarah respects her

The principles of binding limit the relationship between the pronoun and its antecedent by the structure of the sentence – another example of structure-dependency. So that herself can only be bound within a certain part of the structure, that is to say the clause Sarah respects herself. The pronoun her, on the other hand, is free to go outside this limit, so it may be bound to the Noun Phrase Helen in the main clause or to someone else altogether.

However, the Japanese equivalent to herself, ignores this restriction and can be bound outside the clause. Is the principle therefore wrong? Instead, linguists have argued that there is a parameter about what restricts binding in a language. English has a tight restriction on herself, binding it within its own clause; Japanese has a far looser restriction, binding it within the whole sentence. This does not affect all the pronouns in a language, but only particular words. In other words, it is a parameter that belongs to the individual word. Speakers have just to learn which of the settings is possible for a word in a language. The parameter is then a matter of vocabulary, not of grammatical principles. Variation between languages has been put where it belongs – in the lexicon. This is termed the ‘lexical parameterization hypothesis’. So all variation between one language and another, or, more precisely, between the grammar in one person’s mind and that in another’s, whether in vocabulary or parameter settings, is in the lexicon. According to Chomsky we are all speakers of the same language, separated only by our different vocabularies.

To sum up, to acquire a language, learners have to apply the principles of UG to the samples of speech they encounter, set the parameters of the functional phrases, and gain detailed lexical information about masses of lexical items.