A sentence can contain many pieces of information, but those pieces do not all have the same relationship to the words around them.
- Maya put the keys on the table.
- Maya read the report on the train.
Both sentences end with a prepositional phrase. Both phrases answer a question about place. Yet they behave differently.
Put normally demands a destination or location: Maya put the keys feels unfinished. The phrase on the table helps complete the verb’s event structure.
Read, by contrast, can stand comfortably without the train: Maya read the report. The phrase on the train adds circumstance rather than completing the lexical requirements of read.
This is the distinction between complements and adjuncts.
It is one of the quiet load-bearing structures of English. Without it, learners may identify phrases correctly by form but misunderstand why those phrases are there, what can be omitted, what belongs to a verb’s valency, and where ambiguity comes from.
For the larger system, begin with How English Works and the English Learning Hub. This article connects directly to Verb Valency and Argument Structure, Constituent Structure, Small Clauses, and Adverbial Clauses.
The shortest useful definition
A complement is an element selected or licensed by a head—such as a verb, adjective, noun or preposition—as part of its grammatical or semantic pattern. An adjunct is an optional modifier that adds circumstance or descriptive information without being selected in the same way.
That definition immediately needs one qualification: “optional” is not a perfect test. Some complements can be omitted when context makes them recoverable, while some adjuncts can feel pragmatically necessary because a reader needs the information. The distinction is therefore not simply required versus optional.
The deeper question is one of selection: does the head word create a grammatical slot for this element, or does the phrase arrive from the outside as additional scene-setting information?
Start with the verb’s event architecture
Different verbs open different structural slots.
- sleep can describe an event with one participant: Maya slept.
- admire normally introduces an experiencer and an object: Maya admired the painting.
- give naturally introduces giver, theme and recipient: Maya gave Daniel the file.
- put ordinarily introduces an entity moved and a resulting location: Maya put the file on the desk.
These patterns belong to lexical valency. The verb does not merely contribute an action label; it shapes the participant architecture of the clause.
Complements are often the grammatical expressions of those selected participants or states.
Objects are classic complements
- Maya opened the door.
- Daniel understands the problem.
- The committee approved the proposal.
The object is tightly connected to the verb’s meaning. Approve is an act directed toward something approvable; understand relates an experiencer to content; open commonly acts on an affected entity.
Some objects can disappear in context—Have you eaten?, I already know, She is reading—but that does not turn them into adjuncts. The lexical pattern still permits or anticipates an object relation even when the particular complement is left implicit.
This is why the deletion test must be used carefully.
Predicative complements complete states and classifications
- Maya is tired.
- Daniel became a doctor.
- The room remained silent.
The adjective or noun phrase is not merely decorative detail. It completes the predication created by the copular or linking verb.
Maya is can occur in highly specialised contexts, but ordinary English expects a following expression that identifies a state, role or location. In Daniel became a doctor, the noun phrase supplies the result state associated with became.
These are subject-oriented predicative complements.
Object complements create a second predication
- They painted the door red.
- We found the room empty.
- The board elected Maya chair.
The final expression predicates a property or role of the object. The door becomes red; the room is empty; Maya becomes chair.
This connects complement structure to Small Clauses and Resultative Constructions. The important point here is selection: verbs such as consider, find, elect and resultative constructions license a complement that closes a secondary predication.
Prepositional complements can be selected by the verb
- depend on the result
- refer to the diagram
- rely on evidence
- belong to Maya
The preposition is not freely interchangeable. English says depend on, not ordinarily depend at or depend with. The verb helps select the prepositional relation.
This makes the entire prepositional phrase complement-like.
Compare a true adjunct:
Maya relied on the report during the meeting.
On the report belongs to the verb’s lexical relation. During the meeting simply places the reliance event in time.
Clause complements package propositions
- I think that the plan will work.
- She wondered whether the train had left.
- They want to leave early.
The selecting verb opens a slot for content: what is thought, wondered or wanted.
The complement can be finite, interrogative or non-finite. What unifies the examples is not surface form but function: each clause supplies the content selected by the higher predicate.
This connects to Clause Embedding and Complementation.
Adjectives can select complements too
- afraid of the dark
- proud of her work
- ready to begin
- aware that the figures are incomplete
The complement supplies the target, content or domain of the adjective’s meaning.
Proud creates a relation to something that generates pride. Aware creates a relation to informational content. Ready often opens a prospective action slot.
Complementation therefore belongs to heads across grammatical categories, not just verbs.
Nouns can select complements
- the destruction of the bridge
- the belief that the policy will work
- the decision to postpone the launch
Event nouns and abstract nouns can inherit participant or content relations from corresponding verbs.
This links directly to Nominalisation and Event Nouns. A noun phrase can contain its own miniature argument structure.
Adjuncts build the scene around the selected core
Adjuncts commonly express time, place, manner, reason, purpose, condition, frequency, duration and viewpoint.
- Maya read the report on Tuesday.
- Maya read the report in the library.
- Maya read the report carefully.
- Maya read the report because the meeting was tomorrow.
- Maya read the report three times.
The verb read does not select Tuesday, the library, carefulness, tomorrow’s meeting or three repetitions as lexical participants. These expressions enrich the event from outside the verb’s core valency.
Adjuncts are the architecture of circumstance.
The deletion test helps—but does not decide everything
A common diagnostic is to remove the disputed phrase.
- Maya read the report in the library. → Maya read the report. Fine.
- Maya put the report on the desk. → Maya put the report. Usually incomplete.
This suggests in the library is an adjunct and on the desk a complement.
But omission can be context-dependent. Maya already ate omits an object that eat often permits. The meeting lasted may be grammatically complete yet pragmatically invite a duration. Deletion therefore reveals obligatoriness, not selection by itself.
Use several diagnostics together.
The repeatability test
Adjuncts can often be stacked:
Maya read the report in the library on Tuesday after lunch very carefully.
Multiple circumstances can accumulate around the same event.
Selected complements are usually more limited. A verb does not ordinarily take an unlimited sequence of direct objects or selected destination complements.
This makes repeatability a useful, though not absolute, diagnostic.
The preposition-choice test
Selected complements often constrain the preposition:
- rely on
- refer to
- consist of
- comply with
Adjuncts usually allow broader semantic choice:
- in the office
- near the office
- outside the office
- after the meeting
- before the meeting
The word being modified does not lexically dictate those prepositions; the intended spatial or temporal relation does.
The semantic-role test
Complements often correspond to participants built into the event concept: agent, experiencer, theme, recipient, goal, content, result state.
Adjuncts more often express circumstantial roles: time, general location, manner, instrument, reason, frequency or speaker viewpoint.
Again, boundaries are not always clean. Instruments can feel strongly associated with particular actions; locations can be selected by some verbs and merely circumstantial with others. The same semantic label does not guarantee the same grammatical status.
The same phrase type can be complement or adjunct
This is the most important protection against mechanical parsing.
- She put the vase on the shelf. — selected location/result complement.
- She admired the vase on the shelf. — likely modifier locating the vase or event.
- She lives in Singapore. — location closely completes live in many uses.
- She studies in Singapore. — location is more clearly circumstantial.
You cannot label a phrase “adjunct” merely because it is prepositional, nor “complement” merely because it follows the verb.
Grammar is relational.
Attachment ambiguity often begins here
Maya saw the man with binoculars.
Does with binoculars describe the man, or the manner/instrument of seeing?
The phrase can attach inside the noun phrase—the man with binoculars—or to the seeing event—saw using binoculars.
Complement–adjunct analysis therefore intersects with constituent structure and attachment. Before asking what a phrase means, ask what it belongs to.
Complements are usually closer to the head
English often places selected material relatively close to its head, with freer adjuncts further outward.
Maya discussed the proposal with Daniel after lunch.
The direct object is tightly selected. The with-phrase may represent a co-participant. The temporal adjunct sits further out.
This ordering tendency is useful, but English information structure can reorder phrases for weight, focus and discourse needs. Position is evidence, not proof.
Mobility is greater for many adjuncts
- On Tuesday, Maya read the report.
- Maya, on Tuesday, read the report.
- Maya read the report on Tuesday.
Temporal adjuncts often move among several clause positions.
Selected complements are generally less mobile: The report, Maya relied on requires a special topicalisation construction rather than ordinary adjunct repositioning.
Mobility therefore provides another clue to structural status.
Adjunct scope can change with position
Fortunately, Maya found the answer.
Here fortunately comments on the whole proposition.
Maya carefully found the answer is less natural because carefully wants to describe manner, and find is not normally an intentional gradual activity in that reading.
Adjuncts themselves form levels: manner adjuncts, temporal adjuncts, sentence adverbials and discourse-level comments can attach at different structural heights.
This is one reason “adverbial” is a function family rather than a single position.
Complements affect meaning more radically
Change a selected complement and you can change the verb sense itself.
- run a company
- run a program
- run five kilometres
- run into a friend
The structures help determine which lexical sense of run the reader selects.
Adjuncts typically preserve the core sense while adding circumstances: run quickly, run every morning, run in the park.
Complementation therefore participates in lexical disambiguation.
Arguments and complements are related but not identical terms
Different grammar traditions use argument and complement differently.
An argument is usually a semantic or syntactic participant licensed by a predicate. A complement is often a phrase-level grammatical relation to a head. Many objects are both arguments and complements.
But frameworks disagree about whether subjects count as complements, whether certain optional selected phrases are arguments, and where exactly complement ends and adjunct begins.
The productive learner question is not “which terminology wins?” It is “what structural and semantic relationship is this phrase expressing?”
Complements in reading comprehension
Long sentences become easier when readers separate the selected core from the circumstantial layers.
The committee decided, after three hours of debate, in response to the regulator’s request, to postpone the launch.
Strip away the adjuncts:
The committee decided to postpone the launch.
The infinitival complement contains the core content of the decision. The intervening phrases supply time and reason/context.
This is a powerful reading strategy: find the lexical skeleton first, then restore the circumstances.
Complements in writing and editing
Writers often overload a clause with adjuncts until the selected core becomes hard to see.
The company, after months of consultation with suppliers and advisers, during a period of unusually volatile demand, decided, with considerable reluctance, to close the facility.
The grammatical spine is simple: The company decided to close the facility.
Editing becomes easier once the spine is visible. Adjuncts can then be reordered, split into another sentence, or retained where they genuinely help the reader.
Complements and exam grammar
Many examination errors are really selection errors.
- discuss about the issue — standard discuss already selects a direct object; about is usually unnecessary.
- explain me the problem — standard explain typically selects the content plus a to-recipient: explain the problem to me.
- depend of the result — lexical selection requires depend on.
These are not random preposition mistakes. They arise because learners have not yet acquired the complement pattern of the head word.
Teaching vocabulary without valency leaves half the word untaught.
Complements in technical and scientific prose
Technical writing depends on knowing which information is structurally central.
The result depends on temperature. The on-phrase identifies the variable that the dependency relation requires.
The result depends on temperature under laboratory conditions. The final phrase describes the circumstances under which that dependency is being asserted.
Confusing the two can blur causal structure. A selected dependency is not the same thing as a contextual qualifier.
Complements in narrative
Narrative style gains control when the writer understands which details are structurally optional.
Maya put the envelope beneath the loose floorboard before dawn.
Beneath the loose floorboard completes the placement event; before dawn adds temporal atmosphere.
If the writer deletes the location, the placement action loses its destination. Delete the time phrase and the action remains complete but less atmospheric.
This difference gives editors a practical hierarchy when tightening prose.
A compact diagnostic table
| Diagnostic | Complement tendency | Adjunct tendency |
|---|---|---|
| selected by head? | yes | no |
| preposition fixed by head? | often | usually chosen by intended circumstance |
| can many similar phrases stack? | limited | often yes |
| mobility | usually lower | often higher |
| semantic job | participant/content/result | time/place/manner/reason/circumstance |
| deletion | may create incompleteness or implicit argument | usually leaves lexical core intact |
Common learner errors
- Calling every optional phrase an adjunct.
- Calling every phrase after the verb a complement.
- Using deletion as the only test.
- Ignoring lexical preposition selection.
- Failing to distinguish an event participant from a circumstantial detail.
- Misreading attachment because two identical phrase forms can perform different functions.
- Editing away a selected complement and leaving a verb semantically unfinished.
A practical method for students
- Find the head. Which verb, adjective or noun is the disputed phrase attached to?
- Ask what pattern the head selects. Object, preposition, clause, result state, destination?
- Run the deletion test. What happens when the phrase disappears?
- Run the substitution test. Can the phrase vary freely, or is its form constrained by the head?
- Run the mobility test. Can it move like a typical time/place adjunct?
- Name the semantic job. Participant/content or circumstance?
- Use several clues together. Do not let one imperfect diagnostic decide the analysis.
Why complements and adjuncts belong inside How English Works
Complements and adjuncts reveal that a sentence has a centre and a circumference.
The centre is built from lexical relationships: what the verb means, which participants it opens, what content an adjective or noun selects. Around that centre, English can add time, place, reason, manner, frequency and viewpoint almost without limit.
Good readers learn to see both layers at once. Good writers know which details complete the event and which merely decorate or locate it. That difference is not a minor grammar label. It is the difference between the architecture of the proposition and the weather around it.
Teaching Guide
Teach complements and adjuncts by keeping phrase form constant while changing the verb. Compare put the keys on the table with read the report on the table. Ask why the same type of prepositional phrase is central in one sentence but circumstantial in another.
Next, give students four diagnostics—selection, deletion, mobility and repeatability—and insist that they use more than one. Introduce verbs with fixed prepositions so lexical selection becomes visible. Then use long sentences and ask students to strip away adjuncts until the complement skeleton remains.
Finish with editing. Students should take an overloaded paragraph, mark complements in one pass and adjuncts in another, then decide which circumstantial details genuinely help. Mastery means seeing sentence structure as a layered system: selected core first, optional world-building second.
Continue through the English system: How English Works · English Learning Hub · Verb Valency · Constituent Structure