Form-Function Diagram: My mom has bought my sister a gift.

The sentence My mom has bought my sister a gift functions as a declaration. A declaration is a sentence or fragment that conveys information or makes a statement.

The noun phrase my mom functions as the complete subject. The possessive determiner my functions as the determinative of the noun mom. The noun mom functions as the simple subject. A subject is a word, phrase, or clause that performs the action of or acts upon the verb in the predicate.

The verb phrase has bought my sister a gift functions as the complete predicate. The noun phrase my sister functions as the indirect object. An indirect object is a word, phrase, or clause that follows a ditransitive verb and indicates to or for whom or what the action of the verb is performed. The noun phrase a gift functions as the direct object. A direct object is a word, phrase, or clause that follows a transitive verb and receives the action of the verb. The possessive determiner my functions as the determinative of the noun sister. The indefinite article a functions as the determinative of the noun gift.

The predicate also contains the present perfect verb phrase has bought. The auxiliary verb has functions a the perfect. The main verb bought functions as the simple predicate. A predicate is a word or phrase that contains a finite verb and that expresses the action performed by the subject or the state of the subject.

Form-Function Diagram: My mom has bought my sister a gift.

A form-function diagram is a visualization of the layers of grammar. The top identifies forms, or what words, phrases, and clauses look like. The bottom identifies functions, or what words, phrases, and clauses do. For more information about form-function diagrams, see A Form-Function Description of the Grammar of the Modern English Language: Book 1 (Level 9A) (A Form-Function English Grammar) and A Form-Function Description of the Grammar of the Modern English Language: Book 2 (Level 9B) (A Form-Function English Grammar).