Traditional grammar defines the object in a sentence as the entity that is acted upon by the subject. There is thus a primary distinction between subjects and objects that is understood in terms of the action expressed by the verb, e.g. Tom studies grammar—Tom is the subject and grammar is the object. Traditional theories of sentence structure divide the simple sentence into a subject and a predicate, whereby the object is taken to be part of the predicate. Many modern theories of grammar (e.g. dependency grammars), in contrast, take the object to be a verb argument like the subject, the difference between them being mainly just their prominence; the subject is ranked higher than the object and is thus more prominent.
The main verb in a clause determines whether and what objects are present. Transitive verbs require the presence of an object, whereas intransitive verbs block the appearance of an object. The term complement overlaps in meaning with object: all objects are complements, but not vice versa. The objects that verbs do and do not take is explored in detail in valency theory.
Various object types are commonly acknowledged: direct, indirect, and prepositional. These object types are illustrated in the following table:
|Direct object||Entity acted upon||Sam fed the dogs.|
|Indirect object||Entity indirectly affected by the action||She sent him a present.|
|Prepositional object||Object introduced by a preposition||She is waiting for Lucy.|
The descriptions "entity acted upon" and "entity indirectly affected by the action" are merely loose orientation points. Beyond basic examples such as those provided in the table, these orientation points are not much helpful when the goal is to determine whether a given object should be viewed as direct or indirect. One rule of thumb for English, however, is that an indirect object is not present unless a direct object is also present. A prepositional object is one that is introduced by a preposition. Despite the difficulties with the traditional nomenclature, the terms direct object and indirect object are widespread.
The term oblique object is also employed at times, although what exactly is meant varies from author to author. Some understand it to be an umbrella term denoting all objects (direct, indirect, and prepositional), whereas others use the term to denote just a prepositional object.
While the typical object is a pronoun, noun, or noun phrase, objects can also appear as other syntactic categories, as illustrated in the following table:
|Noun (phrase) or pronoun||The girl ate fruit.|
|that-clause||We remembered that we had to bring something.|
|Bare clause||We remembered we had to bring something.|
|for-clause||We were waiting for him to explain.|
|Interrogative clause||They asked what had happened.|
|Free relative clause||I heard what you heard.|
|Gerund (phrase or clause)||He stopped asking questions.|
|to-infinitive||Sam attempted to leave.|
|Cataphoric it||I believe it that she said that.|
A number of criteria can be employed for identifying objects, e.g: The object follows the subject. Languages vary significantly with respect to these criteria. The first criterion identifies objects reliably most of the time in English, e.g.
Fred gave me a book.
- a. A book was given (to) me. — Passive sentence identifies a book as an object in the starting sentence.
- b. I was given a book. — Passive sentence identifies me as an object in the starting sentence.
The second criterion is also a reliable criterion for isolating languages such as English, since the relatively strict word order of English usually positions the object after the verb(s) in declarative sentences.
The third criterion is less applicable to English, though, since English lacks morphological case, exceptions being the personal pronouns (I/me, we/us, he/him, she/her, they/them).
Verbs can be classified according to the number and/or type of objects that they do or do not take. The following table provides an overview of some of the various verb classes:
Number of objects
|Monotransitive||One object||I fed the dog.|
|Ditransitive||Two objects||You lent me a lawnmower.|
|Tritransitive||Three objects||They sold me bananas for two dollars.|
Semantic role of subject
|Unaccusative||Patient||The man stumbled twice, The roof collapsed.|
|Unergative||Agent||He works in the morning, They lie often.|
Ergative and object-deletion verbs can be transitive or intransitive, as indicated in the following table:
|Ergative||The submarine sank the freighter.|
|Object deletion||We have already eaten dinner.|