The subject in a simple English sentence such as John runs, John is a teacher, or John drives a car, is the person or thing about whom the statement is made, in this case John. Traditionally the subject is the word or phrase which controls the verb in the clause, that is to say with which the verb agrees (John is but John and Mary are). If there is no verb, as in Nicola – what an idiot!, or if the verb has a different subject, as in John – I can't stand him!, then 'John' is not considered to be the grammatical subject, but can be described as the topic of the sentence.
The examples and perspective in this article may not represent a worldwide view of the subject. (October 2016)
While these definitions apply to simple English sentences, defining the subject is more difficult in more complex sentences and in languages other than English. For example, in the sentence It is difficult to learn French, the subject seems to be the word it, and yet arguably[according to whom?] the real subject (the thing that is difficult) is to learn French. A sentence such as It was John who broke the window is more complex still. Sentences beginning with a locative phrase, such as There is a problem, isn't there?, in which the tag question isn't there? seems to imply that the subject is the adverb there, also create difficulties for the definition of subject.
In languages such as Latin and German the subject of a verb has a form which is known as the nominative case: for example, the form 'he' (not 'him' or 'his') is used in sentences such as he ran, he broke the window, he is a teacher, he was hit by a motorist. But there are some languages such as Basque or Greenlandic, in which the form of a noun or pronoun when the verb is intransitive (he ran) is different from when the verb is transitive (he broke the window). In these languages, which are known as ergative languages, the concept of subject may not apply at all.