A function in the structure of a clause usually filled by a noun group/phrase (for example, ‘The dog [subject] was barking’). The normal position of the subject is before the verb group/phrase, but in most kinds of interrogatives (questions) it follows the first auxiliary verb (for example, ‘Was the dog barking?’, ‘Why was the dog barking?’).
In main clauses the subject is an obligatory element, except in imperative (command) clauses (for example, ‘Be very tactful’) and in casual style (for example, ‘Want some?’).
Most personal pronouns have a different form when they are the subject of a main clause (for example, I caught the ball. She has the answer etc.), than when they are the object (for example, Max threw the ball to me; Max told me the answer) Similarly ‘Give it to Mary and me’ is correct, not ‘Give it to Mary and I.’).
In the present tense, and the past tense with the verb ‘be’, the verb agrees with the subject in person and number (for example, ‘Her son lives with her’ ‘Her sons live with her’).
Subject matter refers to the topic or theme under consideration.