--- title: "acl: clausal modifier of noun β€” definition and key papers" description: "acl (clausal modifier of noun) is the Universal Dependencies relation that attaches a clause to the nominal it modifies." canonical: "https://research.elamur.ai/free/en/concepts/ud-acl/" --- [Elamur Research](https://md.research.elamur.ai/free/en/) Β· [this page in HTML](https://research.elamur.ai/free/en/concepts/ud-acl/) [home](https://md.research.elamur.ai/free/en/) / [concepts](https://md.research.elamur.ai/free/en/concepts/) / acl: clausal modifier of noun # 🌐 acl: clausal modifier of noun Universal Dependencies Β· 6 key papers Β· [all concepts](https://md.research.elamur.ai/free/en/concepts/) Part of: [πŸ—¨οΈ Natural language processing](https://md.research.elamur.ai/free/en/concepts/natural-language-processing/) Β· [🌐 Universal Dependencies](https://md.research.elamur.ai/free/en/concepts/universal-dependencies/) acl (clausal modifier of noun) is the Universal Dependencies relation that attaches a clause to the nominal it modifies. Examples are relative clauses, participial and infinitival clauses, and content clauses after nouns such as "fact". Also: clausal modifier of noun, adnominal clause, acl:relcl (relative clause subtype) ## What it is In [Universal Dependencies](https://md.research.elamur.ai/free/en/concepts/universal-dependencies/) (UD), every dependent of a nominal is labelled by the kind of phrase it is. A nominal dependent is nmod, an adjectival one is amod, and a clausal one is acl. The label therefore records the phrase type, so no separate constituent annotation is needed ([Marneffe et al. 2021](https://md.research.elamur.ai/free/en/papers/marneffe-2021-universal-dependencies/)). This follows from UD's three basic units. Nominals denote entities, clauses denote events, and modifiers specify either of them ([Marneffe et al. 2021](https://md.research.elamur.ai/free/en/papers/marneffe-2021-universal-dependencies/)). The relation joins two words: - The head is a noun, proper noun or pronoun. - The dependent is the head of the modifying clause. This is usually its verb, or the predicate word if the clause has a copula. Function words such as relativizers, subordinators and infinitive markers attach inside the clause. They are not the head of the acl link, because UD treats content words as heads ([Marneffe et al. 2021](https://md.research.elamur.ai/free/en/papers/marneffe-2021-universal-dependencies/)). ### Neighbouring relations UD consistently separates phrasal dependents from clausal ones, as in the pairs nsubj/csubj and advmod/advcl ([Nivre et al. 2016](https://md.research.elamur.ai/free/en/papers/nivre-2016-universal-dependencies-v1-multilingual-treebank/)). acl is the clausal partner of nmod and amod. It differs from these neighbours as follows: - advcl: the clause modifies a predicate, not a noun. - ccomp and xcomp: the clause is a complement of a verb or an adjective. - amod: the modifier is a single adjectival word rather than a clause. Languages may refine universal relations with subtypes, but they may not add new basic categories ([Nivre et al. 2020](https://md.research.elamur.ai/free/en/papers/nivre-2020-universal-dependencies-v2-evergrowing-multilingual/)). The most widespread subtype is acl:relcl for relative clauses. Some treebanks also use acl:cleft for the clause of a cleft sentence. ## Examples 1. The book that she wrote sold well. Here acl:relcl joins book (head) to wrote (dependent), and "that" depends on wrote. 2. A man carrying a ladder knocked. Here acl joins man to carrying, a participial clause with no relative word. 3. Her decision to resign surprised us. Here acl joins decision to resign, an infinitival clause, and "to" attaches as a marker. A content clause such as "the claim that prices rose" also takes plain acl (claim β†’ rose). The clause states what the claim is, rather than restricting which claim is meant. ## Across languages Because the label is universal, the same construction can be compared across typologically different languages ([Marneffe et al. 2021](https://md.research.elamur.ai/free/en/papers/marneffe-2021-universal-dependencies/)). Languages differ in which clause types carry most of the load. In the [English](https://md.research.elamur.ai/free/en/topics/english/) and [French](https://md.research.elamur.ai/free/en/topics/french/) UD treebanks, the dominant pattern is a noun head with a verb dependent. A pronoun head with a verb dependent comes second in both languages. English shows more noun-to-adjective cases than proper-noun heads, while French has the reverse order. French uses the relation for a larger share of its tokens than English does. Plausible causes are its productive participial modifiers and infinitival constructions with "Γ " or "de", as in "une maison Γ  vendre" ('a house for sale'). Languages with prenominal clauses, such as Japanese and Korean, often keep plain acl. Their noun-modifying clauses do not mark a clear contrast between relative and content clauses, so acl:relcl would impose a distinction the grammar does not draw. The underlying question of which strategies realize which constructions across languages is a current topic in UD theory (Nivre 2025). The same holds for clauses with unusual predicates (Nivre et al. 2026). Work on argument structure bears on how a relativized noun's role is recovered (Zeman 2017). ## In treebanks and research The acl relation goes back to the cross-linguistic version of Stanford dependencies ([Marneffe et al. 2014](https://md.research.elamur.ai/free/en/papers/marneffe-2014-universal-stanford-dependencies-cross-linguistic/)). It was part of the first UD release, whose inventory had 40 dependency types ([Nivre et al. 2016](https://md.research.elamur.ai/free/en/papers/nivre-2016-universal-dependencies-v1-multilingual-treebank/)). Under the v2 guidelines it is one of 37 universal relations ([Nivre et al. 2020](https://md.research.elamur.ai/free/en/papers/nivre-2020-universal-dependencies-v2-evergrowing-multilingual/)). ### Enhanced representation A basic tree cannot show that the head noun of a relative clause is also an argument inside that clause. The enhanced representation is a graph that adds such implicit relations ([Marneffe et al. 2021](https://md.research.elamur.ai/free/en/papers/marneffe-2021-universal-dependencies/)). For English it was specified in detail and released with converters in Stanford CoreNLP ([Schuster & Manning 2016](https://md.research.elamur.ai/free/en/papers/schuster-2016-enhanced-english-universal-dependencies-improved/)). That work served applications that need direct links between content words, such as relation extraction ([Schuster & Manning 2016](https://md.research.elamur.ai/free/en/papers/schuster-2016-enhanced-english-universal-dependencies-improved/)). ### Parsing In [dependency parsing](https://md.research.elamur.ai/free/en/concepts/dependency-parsing/), acl is evaluated like any other label. It is one of the relations tested in the 2017 and 2018 CoNLL shared tasks on parsing raw text ([Marneffe et al. 2021](https://md.research.elamur.ai/free/en/papers/marneffe-2021-universal-dependencies/)). Errors tend to come from three sources: - the attachment site, when a clause could modify either a noun or the verb; - confusion with advcl; - uneven use of subtypes across treebanks. Uneven annotation of this kind is the subject of studies of [treebank](https://md.research.elamur.ai/free/en/topics/treebanks/) consistency in UD ([Marneffe et al. 2017](https://md.research.elamur.ai/free/en/papers/marneffe-2017-assessing-annotation-consistency-universal-dependencies/)). Tutorials on UD principles and tools cover how such clauses should be analysed (Zeman 2021). How often the relation acl occurs: its share of all tokens Counted by code over the Universal Dependencies 2.18 treebanks of English and French (every token once, subtypes with their base relation). **The numbers** | Treebanks | Share | | --- | --- | | English treebanks | 1.43% of tokens (16,121 tokens) | | French treebanks | 2.14% of tokens (23,298 tokens) | What acl joins: the most frequent head tag β†’ dependent tag The five most frequent in each language's treebanks, by tokens. **The numbers** | Pair | Tokens | | --- | --- | | English: NOUN β†’ VERB | 11,890 | | English: PRON β†’ VERB | 1,431 | | English: NOUN β†’ ADJ | 538 | | English: PROPN β†’ VERB | 526 | | English: NOUN β†’ NOUN | 349 | | French: NOUN β†’ VERB | 16,944 | | French: PRON β†’ VERB | 2,927 | | French: PROPN β†’ VERB | 1,405 | | French: NOUN β†’ ADJ | 453 | | French: NOUN β†’ NOUN | 335 | ## Key papers The works this page cites, the most cited first; citations as counted by OpenAlex plus the papers of this library that cite the work, read 2026-10-24. - [Universal Dependencies v1: A Multilingual Treebank Collection](https://md.research.elamur.ai/free/en/papers/nivre-2016-universal-dependencies-v1-multilingual-treebank/) β€” Joakim Nivre, Marie-Catherine de Marneffe, Filip Ginter et al. Β· 2016 Β· 1,741 citations - [Universal Stanford dependencies: A cross-linguistic typology](https://md.research.elamur.ai/free/en/papers/marneffe-2014-universal-stanford-dependencies-cross-linguistic/) β€” Marie-Catherine de Marneffe, Timothy Dozat, Natalia Silveira et al. Β· 2014 Β· 627 citations - [Universal Dependencies](https://md.research.elamur.ai/free/en/papers/marneffe-2021-universal-dependencies/) β€” Marie-Catherine de Marneffe, Christopher D. Manning, Joakim Nivre et al. Β· 2021 Β· 480 citations - [Enhanced English Universal Dependencies: An Improved Representation for Natural Language Understanding Tasks](https://md.research.elamur.ai/free/en/papers/schuster-2016-enhanced-english-universal-dependencies-improved/) β€” Sebastian Schuster, Christopher D. Manning Β· 2016 Β· 336 citations - [Universal Dependencies v2: An Evergrowing Multilingual Treebank Collection](https://md.research.elamur.ai/free/en/papers/nivre-2020-universal-dependencies-v2-evergrowing-multilingual/) β€” Joakim Nivre, Marie-Catherine de Marneffe, Filip Ginter et al. Β· 2020 Β· 325 citations - [Assessing the Annotation Consistency of the Universal Dependencies Corpora](https://md.research.elamur.ai/free/en/papers/marneffe-2017-assessing-annotation-consistency-universal-dependencies/) β€” Marie-Catherine de Marneffe, Matias Grioni, Jenna Kanerva et al. Β· 2017 Β· 30 citations ## Related concepts - [Universal Dependencies](https://md.research.elamur.ai/free/en/concepts/universal-dependencies/) β€” Universal Dependencies is a framework and an open collection of treebanks that annotates the grammar of many languages with one shared… - [Dependency parsing](https://md.research.elamur.ai/free/en/concepts/dependency-parsing/) β€” Dependency parsing is the task of recovering a sentence's syntactic structure as directed, labelled links between its words. Each word is… ## More papers Topics: [🌐 Universal Dependencies](https://md.research.elamur.ai/free/en/topics/universal-dependencies/) Β· [🌳 Dependency parsing](https://md.research.elamur.ai/free/en/topics/dependency-parsing/) Shelves: [πŸ—£οΈ Language and Linguistics](https://md.research.elamur.ai/free/en/shelves/arts-and-humanities/language-and-linguistics/) - [next concept β†’ ADJ: adjective](https://md.research.elamur.ai/free/en/concepts/upos-adj/) - [↑ back to concepts](https://md.research.elamur.ai/free/en/concepts/)