Topic summary
Grammatical Subject
Extracted from the Wikipedia article Subject (grammar).
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.