Here's why:
* Subject: The subject of a sentence is the noun or pronoun that performs the action of the verb.
* Nominative Case: The nominative case is used for the noun or pronoun that is the subject of a verb.
Example:
* Puella librum legit. (The girl reads the book.)
* Puella is in the nominative case and is the subject of the sentence.
* Librum is in the accusative case and is the object of the verb "legit" (reads).
Let me know if you'd like more examples or have any other questions!