The syntactic functions or the members of the sentence are traditionally divided into principal (main)and secondary.
The principal parts of the sentence are the subject and the predicate, which modify each other: the subject is the “person” modifier of the predicate, and the predicate is the “process” modifier of the subject; they are interdependent.
The secondary parts are: the object – a substance modifier of the predicate; the attribute – a quality modifier of substantive parts, either the subject or the object; the adverbial modifier – a quality modifier of the predicate; the apposition – a substance modifier of the subject; the parenthesis (parenthetical enclosure) - a detached speaker-bound modifier either of one of the nominative parts of the sentence or of the sentence in general; the address (addressing enclosure) – a modifier of the destination of the whole sentence; the interjection (interjectional enclosure) – an emotional modifier.