Yes a proper noun can be the subject of a sentence. eg
John left home early this morning. -- John is the proper noun.
That would be the subject of the sentence.
Subject
No, the subject "math" is not a proper noun; it is a common noun. Proper nouns refer to specific names of people, places, or organizations, while common nouns refer to general categories or concepts. "Math" refers to the subject itself and is not capitalized unless it begins a sentence.
The subject of the sentence is the proper noun 'Isabel'.
The nouns in the sentence are:friend, common noun, subject of the sentence;Harry, proper noun, an appositive, renames the noun 'friend';boy, common noun, subject complement, renames the subject noun.
The noun in the sentence is Cindy; a proper noun, the name of a person; the subject of the sentence.
Pencil proper or common noun
Exxon is a proper noun
proper noun
As a name of a road , Park Avenue', it is a proper noun, and both words star with a capital letter. However, when used separately, as 'the park, or 'the avenue', they are common nouns and so not need a capital letter.
The noun Bible (capital B) is a proper noun as the title of the religious text of Christianity. The noun bible (lower case b) is a common noun as a word for a book that is considered the most important one for a particular subject.
The word Easter is a noun, a proper noun, the name of a specific holy day or holiday. A noun can be used as the subject of a sentence or clause, and the object of a verb or preposition. Subject of the sentence: "Easter is tomorrow."