Little pro

In linguistics, in the study of syntax, an empty category is a nominal element that does not have any phonological content and is therefore unpronounced. Empty categories may also be referred to as covert nouns, in contrast to overt nouns which are pronounced. The phenomenon was named by Noam Chomsky in his 1981 LGB framework. Some empty categories are governed by the empty category principle. When representing empty categories in trees, linguists use a null symbol to depict the idea that there is a mental category at the level being represented, even if the word(s) are being left out of overt speech. There are four main types of empty categories: NP-trace, Wh-trace, PRO, and pro. The types are differentiated by their two binding features: the anaphoric feature [a] and the pronominal feature [p]. The four possible combinations of plus or minus values for these features yield the four types of empty categories. Empty categories are present in most of the world's languages, although different languages allow for different categories to be empty.

In the table, [+a] refers to the anaphoric feature, meaning that the particular element must be bound within its governing category. [+p] refers to the pronominal feature which shows that the empty category is taking the place of an overt pronoun.

Not all empty categories enter the derivation of a sentence at the same point. Both NP-trace and Wh-trace are only generated as the result of movement operations. Trace refers to the syntactic position which is left after something has moved, helping to explain how NP-trace and Wh-trace get their names. What is meant by "trace" is that there is a position in the sentence that holds syntactic content in the deep structure, but that is not present at the surface, or S-structure. Conversely, both PRO and pro are not the result of movement and must be base-generated In both the government and binding and minimalism frameworks, the only method of base-generation is lexical insertion. This means that both "PRO" and pro are held to be entries in the mental lexicon, whereas Wh-trace and NP-trace are not categories in the lexicon.

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