In linguistics, the projection principle is a stipulation proposed by Noam Chomsky as part of the phrase structure component of generative-transformational grammar. The projection principle is used in the derivation of phrases under the auspices of the principles and parameters theory. Details Under the projection principle, the properties of lexical items must be preserved while generating the phrase structure of a sentence. The principle, as formulated by Chomsky in Knowledge of Language: Its Nature, Origin and Use (1986), states that "lexical structure must be represented categorically at every syntactic level" (Chomsky 1986: 84). Chomsky further defined the projection principle as "representations at each level of syntax(MF, D, S) are projected from the lexicon in that they observe the subcategorisation properties of lexical items." This refers to the fact that every individual piece of a syntactic structure is part of a particular category (i.e. “John” is a member of the category Noun and “run” is a member of the category Verb). The Projection Principle requires that reference to these categories surfaces at every level of a syntactic phrase structure. This requires a knowledge of arguments and internal structures. “John” may be a noun, but nouns are always dominated by a determiner phrase (DP). The verb “run” does not select for the noun “John”, but rather it selects for the DP “John”. The Projection Principle simply states that when notating the syntactic structure of a sentence such as “John runs fast.”, we must specify at every level what lexical category each piece of the sentence belongs to Two common ways of notating the syntactic structure of a sentence under X-Bar Theory include bracketing and tree drawing. The bracketing for the sentence "john runs fast", generated in line with X-bar Theory, is as follows: [CP[C'[C e][TP[DP[D'[D e][NP[N'[N John]]]]][T'[T_EPP [V run] [T -s]][VP[VP[<DP>[D'[D <e>][NP[N'[N <John>]]]]][V'[ ]]][AP[A'[A fast]]]]]]]] The tree structure that this bracketing generates can be seen in the figure below. With the visual aid of the tree, the projection principle can more clearly be seen. Looking at the word John (in either position) and following it up through the structure We see N (noun), followed by N' (pronounced "N Bar": an obligatory representation of the category resulting from the projection principle and X-bar Theory), followed by NP (Noun Phrase). All three of these levels are seen because the projection principle requires that the category of John, Noun, be represented throughout the structure. The