The Contextors’ Voice Conjugator

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Abstract: This article is concerned with the Contextors Voice Conjugator, a tool for changing the voice of English sentences from active to passive and vice versa. We show how our Voice Conjugator benefits from taking as input the syntactic structures assigned to sentences by our parser. We also demonstrate the importance of constraints on syntactic structure to the successful application of the Voice Conjugator.

The Contextors Voice Conjugator is a tool for changing the voice of English sentences from active to passive and vice versa. It is based on Contextors’ syntactic parser, which assigns to sentences of English constituent structure trees where the nodes are annotated with syntactic category labels and grammatical function labels.

Constituent structure and voice identification

The constituent structure of a sentence is useful in changing its voice. Consider first the task of identifying the voice of the input sentence. Passive sentences in English contain some form of the auxiliary be, and their main verb is in the past participle form. But meeting these two conditions does not guarantee that the sentence is in the passive, as the sentence in (1) demonstrates.

(1) Having been shot has damaged him.

The sentence in (1) is in the active, even though it contains a form of the auxiliary be (been) and its main verb damaged is in the past participle form. What is missing in our characterization of passive sentences in English is the requirement that auxiliary be and the verb phrase headed by the main verb combine to form the verb phrase whose head is be. In (1’), the constituent structure tree of (1), it is the auxiliary has, not been, that combines with the verb phrase headed by damaged. (The subject of (1), having been shot, is a passive clause where been combines with the verb phrase headed by shot to form the verb phrase been shot.)

(1’)

declarative_clause
gerund_participial_clause
verb_phrase (gerund_participial)
verbhaving
verb_phrase (past_participial)
verbbeen
verb_phrase (past_participial)
verbshot
verb_phrase
verbhas
verb_phrase (past_participial)
verbdamaged
noun_phrase
nominal
nounhim
The syntactic structure tree of the sentence having been shot has damaged him. From the tree we can see that the verb phrase immediately below the declarative clause is not passive, since it does not combine with passive be.

Based on the constituent structure in (1’) then, our Voice Conjugator correctly analyzes the sentence in (1) as an active sentence and generates its passive counterpart as in (2).

(2)

he has been damaged by having been shot

Constituent structure and voice transformation

The constituent structure of the sentence is also useful in carrying out the voice transformation itself, since it is sentence constituents that change their position when switching from one voice to another. If a sentence is ambiguous, it may also have several counterparts in the voice it is switched to. Consider first the active sentence in (3).

(3) They brought many beautiful presents.

(3) is syntactically ambiguous: it may mean that many beautiful presents were brought or else that many (people) were brought beautiful presents (note that we use the passive voice in order to disambiguate the sentence). Our Voice Conjugator is sensitive to the dependency of voice transformation on the syntactic structure of the sentence. We therefore get the results in (3’) and (3’’):

(3’)

many beautiful presents were bought by them
sentence
subject
nounthey
predicate
predicator
verbbrought
direct_object
determiner
determinativemany
internal_pre_modifier
adjectivebeautiful
nounpresents
The syntactic structure of (3) where the string many beautiful presents is one noun phrase with the grammatical function of direct object.

(3’’)

many were brought beautiful presents by them
sentence
subject
nounthey
predicate
predicator
verbbrought
indirect_object
fused_determiner_head
determinativemany
direct_object
internal_pre_modifier
adjectivebeautiful
nounpresents
The syntactic structure of (3) where many has the grammatical function of indirect object.

In the tree in (3’), the direct object is the noun phrase many beautiful presents, and this noun phrase is moved to subject position in the passive. In the tree in (3’’), the determinative many form a noun phrase on its own (we follow Payne and Huddleston (2002) in analyzing it as what they call a ‘fused determiner-head’1). The passive is now formed by moving the indirect object many to subject position.2

Another type of ambiguity that is successfully handled by our Voice Conjugator occurs when the by-preposition phrase in a passive clause can be attached to either the main verb phrase or else an embedded verb phrase. This is exemplified by the sentence in (4).

(4) The manager was allowed to be interviewed by the committee.

On the reading corresponding to the structure where the by-preposition phrase3 is attached to the main verb phrase (was allowed to be interviewed), the committee allowed the manager to be interviewed (by an unspecified person or group of persons). On the reading corresponding to the structure where the by-preposition phrase is attached to the embedded verb phrase (be interviewed), some person or another allowed the manager to be interviewed by the committee.

(4’)

the committee allowed the manager to be interviewed
sentence
subjectthe manager
predicate
predicator
verbwas
catenative_complement
predicate
predicator
verballowed
catenative_complement
predicate
subordinatorto
predicator
verbbe
catenative_complement
predicate
predicator
verbinterviewed
internalised_complementby the committee
The syntactic structure of (4) where by the committee designates who allowed the manager to be interviewed.

(4’’)

someone allowed the manager to be interviewed by the committee
sentence
subjectthe manager
predicate
predicator
verbwas
catenative_complement
predicate
predicator
verballowed
catenative_complement
predicate
subordinatorto
predicator
verbbe
catenative_complement
predicate
predicator
verbinterviewed
internalised_complementby the committee
The syntactic structure of (4) where by the committee designates who interviewed the manager.

Keeping track of the number of complements of the verb

Our syntactic parser and Voice Conjugator are sensitive not only to constituent structure but also to the number and types of complements a verb has in the sentence and to whether they match the number and types of complements specified for it in the lexicon. Consider the sentence in (5).

(5) This plan was run by the manager.

Even though this is a passive sentence, it has a reading (maybe its only reading) where the by-preposition phrase is not used to designate the agent of the activity described by the sentence, but is a complement of the verb run. This reading is generated by the lexical entry of run that means, according to the Oxford Dictionaries Online4, “tell (someone) about something, especially in order to ascertain their opinion or reaction”. This entry of the verb takes as complements a noun phrase and a by-preposition phrase.

Our syntactic parser uses the “get-someone’s-opinion” lexical entry of run as one of the lexical entries of the verb around which a parse for (5) is built. If a verb is in the active, our parser only accepts parses in which all the complements specified for the verb in the lexicon are part of its verb phrase; if a verb is in the passive, our parser only accepts parses in which exactly one of the noun phrase complements is missing from the verb phrase. (5) is a passive sentence in which one argument of run on its “get-someone’s-opinion”-meaning is missing from the verb phrase: this is the direct object, which moved to the subject position in the passive sentence (5). The by-preposition phrase in (5) must be a complement of run (on the relevant reading) and cannot be used to designate the agent of the activity described. When our Voice Conjugator takes over, it gets as input a syntactic tree where there is no by-preposition phrase that is labeled as an ‘internalised complement’ (as said in endnote 2, we use the term ‘internalised complement’ for the by-preposition phrase containing the noun phrase that serves as subject in the active sentence); it therefore resorts to assigning the role of subject of the active sentence generated from (5) to the string someone/something.

The syntactic tree of (5) under the reading just discussed and the active sentence constructed by the Voice Conjugator are given in (5’).

(5’)

someone/something ran this plan by the manager
sentence
subject
determiner
determinativethis
nounplan
predicate
predicator
verbwas
catenative_complement
predicate
predicator
verbrun
prepositional_complement
prepositionby
preposition_complement
determiner
determinativethe
nounmanager
The syntactic structure of (5). By the manager is here a complement of the verb run, not an internalised complement.

To conclude, we mention one more thing our Voice Conjugator can do that allows it to do its job, namely retrieve different nodes in the tree and their properties. For example, it can access the information that the direct object in the sentence in (6) consists of the string him and that it is a third person singular pronoun in the accusative case.

(6) They have seen him.

When the pronoun him is promoted to subject position in (7), the passive counterpart of (6), our Voice Conjugator is able to retrieve the nominative form of the third person singular pronoun and the third person singular form of the auxiliary have, so that the latter agrees with the former (in addition, it changes they to them).

(7) He has been seen by them.

Conclusion

What we have shown then is that in transforming sentences of English from active to passive and vice versa, the Contextors Voice Conjugator relies on constituent structure, lexical properties of specific nodes, and global information derived from both these sources.


References
Payne, John and Rodney Huddleston (2002) ‘Nouns and noun phrases’. Chapter 5 in Rodney Huddleston and Geoffrey K. Pullum, eds., The Cambridge Grammar of the English Language. Cambridge University Press. Pp. 323-523.

Ward, Gregory, Betty Birner and Rodney Huddleston (2002) ‘Information packaging’. Chapter 16 in Rodney Huddleston and Geoffrey K. Pullum, eds., The Cambridge Grammar of the English Language. Cambridge University Press. Pp. 1363-1447.


  1. We follow Payne and Huddleston in assuming that many in (5b) functions both as the head of the noun phrase and as its determiner. We do not exactly follow the syntactic structure they assume, however (see Payne and Huddleston, section 9).

  2. There is another passive sentence that can be derived from (3’’): by moving the direct object beautiful presents to subject position we get Beautiful presents were brought many by them. This type of sentence (whose subject is the direct object of the corresponding active sentence, which, in turn, contains also an indirect object) is only marginally grammatical, and we therefore do not generate it.

  3. Following Ward, Birner and Huddleston 2002, we use the term ‘internalised complement’ for the by-preposition phrase containing the noun phrase that serves as subject in the active sentence.

  4. The Oxford Dictionaries Online: http://oxforddictionaries.com

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