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An adjective is a part of speech characteristically used to express properties and modify nouns. It can also occur in predicative constructions, as in The cube is red. Its classification depends on its grammatical behavior, beyond whether its meaning sounds descriptive.^[ref]

In an original simple formal semantics, let red objects form $R=\{1,2\}$ and cubes form $C=\{2,3\}$. The expression red cube can denote the intersection $R\cap C=\{2\}$. This illustrates how an adjective can contribute a property to a noun phrase, while leaving the grammatical classification distinct from that particular semantic rule.

Modification alone is insufficient evidence for adjective status. In the Universal Dependencies scheme, a noun used to modify another noun in a compound remains tagged as a noun. Clear category criteria make linguistic annotation reproducible instead of treating every modifier as the same class.

A determiner is a grammatical category whose members help specify the reference of a noun phrase in context. They can signal distinctions such as definite versus indefinite reference, proximity or quantity. Their contribution differs from the descriptive property supplied by a typical adjective.^[ref]

Compare a red box, the red box and this red box. The descriptive words can remain fixed while the expressions impose different expectations about identifying the referent. In a display with several red boxes, pointing can help interpret this, while an earlier mention can help establish the intended referent of the.

Classification also requires a stated scheme. Universal Dependencies includes articles such as a and the under DET, but uses a separate numerical label for cardinal numbers. A familiar broad description like “a word before a noun” is therefore too weak to reproduce the intended linguistic annotation.

A grammatical constituent is a unit that participates as a component of a larger grammatical construction. Constituency describes hierarchical grouping, so adjacency alone does not establish that an arbitrary sequence of words forms one unit. Different levels of an analysis can contain constituents of different sizes.^[ref]

In The red kite rose, a conventional analysis groups the red kite as a noun phrase and assigns it the subject relation. Replacing the whole group with it gives It rose, providing one structural diagnostic. The example separates the number of written words from the number of units occupying that grammatical position.

A useful analysis combines several diagnostics and states the construction under consideration. Context can license omissions or exceptional patterns, so one substitution does not prove every proposed grouping. Grammatical constituents provide the units of a theory of syntax; judgments and controlled comparisons supply evidence for choosing among theories.

A noun is a part of speech whose members commonly name entities or concepts and head noun phrases. Meanings alone do not supply a complete classification: a noun can name an event or property as readily as a physical object. Distribution and inflection provide additional grammatical evidence.^[ref]

For example, explosion names an event, but behaves as a noun in the explosion and two explosions. Its connection with an event does not make it a verb; compare The shell exploded. Likewise, redness is a noun even though it names a property associated with the adjective red.

In Universal Dependencies, the tag NOUN is reserved for common nouns, with PROPN used for proper nouns. That distinction matters when reproducing an analysis: a count of every traditionally named noun is not necessarily a count of only tokens tagged NOUN.

A noun phrase is a grammatical unit conventionally analyzed as headed by a noun, potentially together with dependents that modify or specify it. A single noun or pronoun can also form a minimal noun phrase under this analysis.^[ref]

In The small bird landed, the words the small bird form a noun phrase containing the head bird, the adjective small and a determiner. The whole unit occupies the subject position. Replacing it with it gives It landed, illustrating that a multiword expression can occupy a position also available to one word.

Such substitution is useful evidence for a grammatical constituent, but one test alone does not settle every structural question. A clear syntax states how the proposed head and dependents combine and tests the same account across further constructions. Counting spaces therefore measures a different property from counting noun phrases.

A pronoun is a member of a grammatical category whose uses commonly occupy nominal positions while their interpretation is recovered from context. A previous noun phrase can supply that context, but is not required: I can identify the current speaker without repeating an earlier name.^[ref]

Consider The robot moved beside the box. It stopped. Under a stipulated reading where both objects are possible referents, the spelling it alone does not select one. Grammatical number and syntax can constrain the possibilities while leaving a contextual decision unresolved. The category of the expression and the identity of its referent are distinct annotation questions.

The border with determiners also depends on the adopted scheme. Universal Dependencies documents PRON and DET using characteristic distribution and language-specific conventions. An explicit inventory helps compare text corpus annotations without assuming that a familiar label always covers exactly the same words in every language.

A subject is a grammatical relation identified through language-specific structural tests, such as word order and grammatical agreement. It often corresponds to the actor in a simple active clause, but that semantic association is not its definition. A noun phrase can be a subject without describing an intentional action.^[ref]

Compare A gust broke the branch and The branch was broken by a gust. The first has a gust as its subject; in the passive voice version, the branch has that relation. The participants' involvement in the event has not simply exchanged places. Separating grammatical relations from thematic roles explains the contrast.

In Universal Dependencies, a nominal passive subject can receive nsubj:pass, explicitly preserving its subject status. Such a representation supports a testable structural account and prevents a procedure from assigning “subject” solely to whichever expression appears to name a doer.

A syntactic head is the element treated as central to a construction under a specified structural analysis. It can determine grammatical properties or which other elements may occur. Headedness therefore concerns relationships within a construction, beyond which word seems most informative in the conversation.^[ref]

In a conventional noun-headed analysis of the small boxes, boxes heads the noun phrase. The head's plural grammatical number helps explain the grammatical agreement in The small boxes are ready. Changing small to heavy changes the description without changing that number requirement.

In a dependency representation, a head also provides the attachment point for syntactic dependencies. A reproducible analysis states its conventions: different grammatical frameworks can choose different heads for some constructions. The success of a representation depends on the patterns it explains and predicts, not solely on whether its links form a mechanically valid rooted tree.