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:
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 help 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:
A number of criteria can be employed for identifying objects, e.g: