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Function vs. Category

Differentiate what a word does from what it is called


X structure diagram
leaf fall
We saw some colorful leaves on the ground.
► How does word function differ from word category? ▼ Function vs. Category

A grammatical function:

  • is what a particular word, phrase or clause does, the role it serves in a phrase —head or dependent (determiner, marker, modifier) or in a clause—subject, predicate, complement, adjunct, supplement. See bold-red words under "clause" in the above diagram link.
  • may take form with a word, phrase or clause. For example, a subject could be a noun (Leaves fell.), a noun phrase (The colorful leaves fell.), a gerund clause (Watching leaves fall is relaxing.) or a clause (That leaves fall is completely normal.)

A word category:

  • is what a particular word is called, "part of speech"Noun (N), Verb (V), Adverb (Adv), Adjective (Adj), Preposition (P). A word category includes words that function in a similar way within a clause. 
  • includes phrasal categories, which are like word categories but contain more than one word and, in the case of a prepositional phrase, may include a clause complement.—Noun Phrase (NP), Verb Phrase (VP), Adverb Phrase (AdvP), Adjective Phrase (AdjP), Prepositional Phrase (PP), Determinative Phrase (DP).
  • includes words that share properties. Words in a category function in a similar way. They can be tested for "properties" of the category. See examples Adjective Properties, Adverb Properties, Noun Properties, Preposition Properties, Gerund-Participle.

Word Functions in a Clause

Understand the multiple uses of words, phrases and clauses


Grammatical Function — how a word, phrase or clause is used in a sentence



The subject is usually the cause, agent or doer of the action

but may also be the experiencer of a state or thing undergoing a change ("be" or static verb).

but may also be the thing (person, concept, entity) that we choose to place in the subject position (as in passive voice, or it, there, ).

but may also be understood, not mentioned.

The subject is usually a noun phrase but may be a subordinate clause.

A number of words, phrases and structures can function as the subject of a clause.

The leaves fell on the ground.  (Noun Phrase)

Charlie raked the leaves.  (Proper Noun)

The leaves were raked by Charlie.  (Noun Phrase) passive voice

He raked the leaves.  (Pronoun)

What we saw was spectacular.  (What Phrase)  static verb

That the leaves are so colorful is amazing.  (That Cls)

Raking leaves is good exercise.  (Gerund Cls)

To see this miracle of nature is awesome.  (Infinitive Cls)

It was amazing to us that the leaves were so red.   ("It" as Subject Placeholder)

It was raining.  (It vs. There)

There were so many leaves.  (There)

Rake up the leaves.  (Commands)  subject understood, not mentioned

Predicate/Predicator (Pred)

The predicate is the action or change in state.

A number of verb forms and verb groups serve as the predicate of a clause.


Leaves fall.   (Verb)

The leaves appear red.  (Static Verb)

Leaves are falling.   (Verb Group)

Leaves may fall.  (Modal Verb Group)

The leaves were raked by Charlie. (Passive Verb Group)

Leaves are falling on the ground.  (Verb Phrase)

Complement (Comp)

A complement is a word, phrase or clause that is expected or required to complete the meaning of some other element or structure in the clause. That is, the clause or phrase would not sound complete without the word, phrase or clause.


A number of elements and structures can serve as complements.

Charlie raked the leaves.  (Noun Phrase–Direct Object)

I gave Charlie the rake.  (Noun–Indirect Object)

Charlie put the leaves in the compost bin. (Noun Phrase Complement in Prep Phrase)

The leaves are pretty.  (Adjective–Predicate Complement)

The leaves are maple.  (Noun–Predicate Complement)

The leaves fell on the ground.  (Prepositional Phrase)

We enjoy seeing the colorful leaves.  (Verb + Gerund )

We wanted to see the colorful leaves.  (Verb + Infinitive )

Maple trees do remarkably well here.  (Adverb Complement)

We know that leaves had fallen overnight.  (Clause Complement to a Verb)

Charlie left rather than waiting for us. (Ger Cls Complement in Prep Phrase)

Water that he drank last night made him sick. (Restrictive Clause Complement to a Noun)


An adjunct is an element that is not required to complete the meaning of the clause; it can be omitted and the clause sounds complete (makes sense).  An adjunct adds modifying information to the clause—mostly adverbs and prepositional phrases.

Charlie raked the leaves quickly.  (Manner Adverb)

Charlie raked the leaves often.  (Frequency Adverb)

Charlie really raked the leaves well.  (Degree Adverb)

Charlie raked the leaves into a pile.  (Prep Phrase)

Charlie only raked the leaves in front. (Focus Adverb)

Trees drop their  leaves when the weather is cold. (Connective Prep Phrase)

Trees drop their leaves before winter sets in. (Connective Prep Phrase)

Trees drop their leaves because they need to conserve energy. (Connective Prep Phrase)


A supplement is an extra comment in the form of a word, phrase or clause. It is loosely related to the idea of the main (matrix) clause. It is separated by comma(s), parentheses or dash(es). 

Who, do you think, raked the leaves?   (Clause–Comments)

By the way, Charlie raised his hand.  (Phrase–Adv for Speech Acts)

Hopefully, Charlie knows the answer. (Adverb–Adv for Evaluation)

A wunderkind (very intelligent child) requires special education. (Phrase–Explaining)

Charlie can do it all—repairman, gardener, engineer. (Noun Phrase–Set off Elements, Examples)


Also see Word Functions – Subject, Predicate Complement, Adjunct and Supplement or Modifiers or Determiners.

(Huddleston & Pullum 4 §3)

A Predicate:

Note: Subject-verb is a term often paired like salt and pepper.  To be precise, we should pair subject with predicate (and noun with verb).


Word Functions: Subj – subject; Pred – predicate/predicator; Compcomplement: an element or elements required by a word or structure to complete its meaning in the clause (e.g., DO – direct object; IO – indirect object; PP - prep. phrase);  Adjunctadjunct: elements not required by an expression to complete its meaning (Subord – subordinator; Coord – coordinator); Suplsupplement: a clause or phrase added onto a clause that is not closely related to the central thought or structure of the main clause.



Word Categories (lexical categories)

What a word, phrase, or clause is called

raking leaves

Word Category—"Part of Speech"


Noun (N) 

Nominal (Nom)¹ 

Noun Phrase (NP)

(Noun Properties)


Leaves fell.  (Subject)

We raked the leaves. (Direct Object)

Charlie showed me the leaves on the ground. (Indirect Object)

Charlie walked on the leaves. (Object of Preposition)

Charlie put them in the leaf bin. (Modifier)

Verb (V)

Verb Phrase (VP)

(Verb Properties)

The leaves are colorful. ("Be" Predicate Copula)

The leaves fall. (Predicate)

The leaves are falling. (Predicate)

The leaves have been falling. (Predicate)

Adjective (Adj)

Adjective Phrase (AdjP)

(Adjective Properties)

They are colorful leaves.  (Modifier)

Pigments turn the leaves red. (Object Complement)

The very colorful leaves occur in October.  (Modifier Phrase)

The more colorful leaves belong to the Japanese Maple.  (Modifier Phrase)

Adverb (Adv)

Adverb Phrase (AdvP)

(Adverb Properties)

Charlie raked slowly. (Manner Adverb)

Charlie arrived early. (Time)

Charlie raked there. (Location)

Charlie worked much too slowly. (Intensifier / Degree Adverb)

Preposition (P)

Prepositional Phrase (PP)

(Preposition Properties)

The leaves floated down. (Location)

The leaves floated to the ground. (Location)

Charlie put off raking up the leaves (Particle–Phrasal Verbs)

Charlie raked the leaves in order to clean up the yard. (Prep Phrase [reason])

Charlie raked up the leaves in a flash. (Expressions)

Trees drop their  leaves because of the cold weather. (Adjunct Prep Phrase)

Trees drop their leaves because they need to conserve energy. (Adjunct Prep Phrase)

Determiner (D)

Determinative Phrase (DP)


The leaves fell over the period of a month. (Article)

Some leaves fell last week. (Indefinite Quantity)

These leaves fell last night. (Demonstratives)

Its leaves fell off. (Possessive Pronoun)

Almost every leaf had fallen. (Determinative Phrase)

Subordinator (Subord)

We know that [the leaves will turn brown]. (That-clause)

Charlie wants to [do the right thing]. (infinitival subordinator)

It is important for [Charlie] to [do the right thing]. (subject subordinator in infinitival clause)

Coordinator (Coord)

We were raking and putting the leaves in the leaf bin. (Coordinator)

They were raking leaves, and we were putting them in the compost bin. (Coordinator)

Interjection (Interj)

Oh man! Look at that. (Speech Acts, Interjections, Aside Comments, Discourse Markers)


¹ Nominal an intermediary category between Noun and Noun Phrase:  N leaves; Nominal colorful leaves; NP the colorful leaves. This term often occurs in diagramming and refers to sub-groupings of modifiers and complements within a noun phrase.  See diagram in the next section.

(Huddleston1§4.2.2) (Payne 7.2)

Also see A Clause: examine the parts that make up a clause.


Word Categories: N – Noun; V – Verb; Aux – Auxiliary; Adj – Adjective; Adv – Adverb; P –Preposition; Det –Determiner. See Word Categories.

Phrasal Categories: NP – Noun Phrase; VP – Verb Phrase; AdjP – Adjective Phrase; AdvP – Adverb Phrase; PP – Prepositional Phrase; DP – Determinative Phrase.

Clausal Categories: Cls – clause; F – finite clause; NF – nonfinite clause: Ger – gerund, Inf – infinitive, PPart – past participle.





Linear Labeling

Marking function and word category

Tree diagram

Linear labeling for function and category

Trees are often helpful for visualizing sentence structure. A sentence can also be labeled in a linear manner. For example, the function and category [function–word category] can be inserted after each word, phrase or category. Labeling will vary depending on the amount of detail desired.


We [SubjN]

saw [Pred–V] 

some [Det–Quant]

colorful [Mod–Adj]

leaves. [Comp(DO)–NP]

He [Subj–N]

always [Comp–Adv]

raises [Pred–V]

his hand [Comp(DO)–NP]

before me. [Adjunct–PP]

Charlie [Subj–N]

very quietly [Comp–AdvP]

told [Pred–V] 

me [Comp(IO)–N]

the answer. [Comp(DO)–NP]

The boy [Subj–NP] / [Subj–NP(Det+N)]

who shouted [Comp–RelCls]

is sitting [Pred–VP] 

next to you. [Adjunct–PP]


Some of the boys [Subj–NP] or [Subj–NP(Quant+PP)]

were annoyed [Pred–VP] or [Pred–VP(Pasv)]

by Charlie's behavior. [Adjunct–PP]



Adjective (Adj)

Complement–NP (IO) is an indirect object

Complement–NP (DO) is a direct object

Mod — modifier

Quant — quantity

Rel Cls — relative clause / modifying clause to a noun

Subject / Predicate  Diagrams


Other Terms


Head  (word function)

refers to the primary word in a phrase; it is called "head" because of (1) its primary (initial) position in the phrase, or (2) its primary role (meaning) in the phrase.    See Phrase.

Complement (word function)


Adj (adjective) Adv (adverb) N (noun); NP (noun phrase); PP (prepositional phrase); V (verb)

PRED (function: predicate) consists of a verb, verb group

refers to a word, phrase, or clause that is required to complete another element in the clause. Complements occur with a number of word categories. See Complement.

A complement may be be positioned after the element it completes, post-position:

He read the book. (The predicate has a noun phrase as its complement)

He is looking over the book. (PRED has a NP as its complement)

He referred to the news report. (PRED has a PP as its complement)

He fell on the stairs. (PRED has a PP as its complement)

The fact that he is here is a miracle. (NP has a clause as its complement)

Jill went in place of me. (PP has a PP as its complement)


A complement may also be positioned before the element it completes, pre-position:

They divided the money fairly evenly. (Adv has an Adv as its complement)

They placed me exactly in the middle. (PP has an Adv as its complement)

He's a criminal lawyer. "dishonest". (NP has an Adj as its complement)

He's a criminal lawyer "lawyer for criminal law" (NP has a N as its complement) See Nouns as Modifiers: range of meaning.

Coordinator (word function)

He doesn't know what to do, nor do I. (for, and, nor, but, or, yet)

He walks foggy weather, but I only walk when it's sunny.

Modifier (word function)

refers to a word or phrase that changes or adds information about: the intrinsic quality of a noun (brown leaves); the manner, degree, frequency of an verb (float softly); the limitation of a prepositional phrase (exactly in the middle); the focus of a word (only when I say so);  the intensity of a manner or frequency adverb (quite often shouts); and so on. See Phrase or Modifiers to Nouns.

Nominals (word category)

is an intermediary category between Noun and Noun Phrase:  N leaves; Nominal colorful leaves; NP the colorful leaves. This term is often seen in diagramming and it refers to sub-groupings of modifiers and complements within a noun phrase.  See diagram above in this section.





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Grammar Notes (Advanced)

Traditional and Linguistic Description



Traditional / ESL and Linguistic Descriptions


In traditional grammar, a clause is constructed with a subject and a verb.  The subject may consist of additional modifiers: determiner, adjective, prepositional phrase, adjective phrase, etc.  The verb is either dynamic or stative.  Dynamic verbs take adverb modifiers, stative verbs do not. The verb is either intransitive (does not accept an object) or transitive (accepts an object).  If it does accept an object, then the object can also take additional modifiers.

In traditional grammar, when a noun has a modifier, the word "adjective" is used both for the "part of speech" and for the function (of modifying). No distinction is made between category (part of speech) and function (a relational concept).  For this reason, in current grammar descriptions, one does not say "adjective clause" (a clause cannot be an adjective, but a clause can function as a modifier) or "a noun used as an adjective" (a noun cannot be an adjective, but a noun can function as a modifier).

Azar, Murray and Swan do not cover function vs. category (in the texts cited below). Instead, they present examples in patterns. Swan's text covers words as alphabetical entries with examples but does not specifically focus on function vs. category. (Swan 509)

Also see Diagrams.


In current linguistic description, a clause includes a subject and a predicate which are respectively realized with a noun phrase (NP) and a verb phrase (VP).  A NP consists of a head noun and determiners (if required) and modifiers (optional).   The head governs (determines) the dependents, elements that can be added to the noun phrase . "The head of a clause is realized by a verb phrase VP. And the head of the VP is realized by a verb. "The verb thus functions as the ultimate head of the clause, and is the syntactically more important element within it: properties of the verb determine what other kinds of elements are required or permitted."  (See Huddleston  for a more precise and complete summary. "Sentence and Clause" 2.1–8) (Aarts Ch2 –4)

CATEGORIES:  NPnoun phrase; Nnoun; VP – verb phrase; Vverb; Detdeterminer; PPprepositional phrase; Ppreposition; AdvPadverb phrase; Advadverb; AdjPadjective phrase; Adj – adjective

FUNCTIONS: Subject: Subject,  Predicate: Predicator (V) Complements: (an element or elements required by a word or structure to complete its meaning in the clause), Object, Indirect Object, Predicative Complement Adjuncts: (optional modifiers) Adj, AdjP, Adv, AdvP, PP; Supplements: interpolations and appendages (extra comments not central or essential to the clause)

See Subject–Predicate–Complement (functions).




Works Cited

  • Aarts, Bas. Oxford Modern English Grammar. Oxford UP, 2011.
  • Azar, Betty Schrampfer, and Stacy A. Hagen. Understanding and Using English Grammar. 4th ed., Pearson Education, 2009.
  • Huddleston, Rodney D., and Geoffrey K. Pullum. The Cambridge Grammar of the English Language. Cambridge UP, 2002.
  • Murphy, Raymond. English Grammar in Use. 5th ed., Cambridge UP. 2019.
  • Payne, Thomas Edward. Understanding English Grammar: A Linguistic Introduction. Cambridge UP, 2011.
  • Swan, Michael. Practical English Usage. 3rd ed., Oxford UP, 2005.