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.