science

Projection principle

Projection principle is a science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Projection principle rather than just read about it. In short: 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.

Key takeaways

Projection principle belongs to science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Projection principle to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Projection principle from memory before moving on to harder problems.

Reference excerpt

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 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'[⟨V⟩ ⟨run⟩]]][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 verb run has an obligatory argument, its subject (a DP agent), which must appear in the sentence. The following subcategorization frame for the verb run specifies its properties. The subcategorization frame of run is as follows:

run Verb, [DP agent __ ] An adverb such as fast has its own subcategorization frame: fast Adverb, [VP_] It is out of this frame that a sentence like the following can be generated:

John runs fast. If either of these subcategorization frames are violated, so is the projection principle, and the utterance would be ill-formed:

*Runs fast. *John fast. Before the projection principle was proposed, phrase structures were generated in separation from the properties of lexical entries. These were hypothesized to enter the slots in pre-generated structures waiting to be filled by the lexical material. According to more recent theories, phrase structures are not generated by phrase structure rules, but are "projected" from the lexical entries. The projection principle therefore obviates the need for phrase structure rules in the generative component. In 1982, Noam Chomsky proposed the extended projection principle as an addendum to the projection principle.

Locality of Selection Locality of Selection states that properties of lexical items must be satisfied locally within their domain. The local domain is characterized by being the smallest XP with a subject (WP). The properties of the constituent are chosen by the constituent head. A constituent will be incorrect if the lexical requirements are not satisfied. Locality of Selection ensures that when the projection principle occurs, it is satisfied locally (This explains why in the above example; N, N', and NP appear immediately above John). We see examples of this with certain verbs. With a verb such as “hit” you need a DP that it selects for: *Mary hit Mary hit [DP the ball] In a local domain there are three main levels. The head (X) of the local domain is at the bottom which projects up to and X bar level and then to the XP level. Each head can select for a complement. The X bar level can select for a specifier and the XP level can select for an adjunct. This makes up the basic structure of a local domain. The components of the tree are organized hierarchically. Along with this, the adjunct (YP), specifier (WP) and complement (ZP) are all optional and only used when required

… excerpt ends here. Continue reading the full article.

Illustrations

Worked examples

Example 1 — a first encounter with Projection principle

Start with the simplest possible case. Write down what Projection principle claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Projection principle before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Projection principle ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Projection principle

In research: Projection principle appears in science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Projection principle in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Projection principle is common in secondary-school and first-year university syllabi. It links to neighbouring topics Grammar, Noam Chomsky, so understanding it makes those chapters shorter.
In everyday life: Look for Projection principle outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Projection principle in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Projection principle means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Projection principle out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Projection principle in simple terms?

Why does Projection principle matter?

Because it connects several science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Projection principle?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Projection principle.