Confused by when to use “which” and when to use “that”? Here’s the transcript from the latest Grammar Girl podcast. Here’s a freebie for Greek and Latin students. If you understand the difference between the nominative case and the accusative and dative cases, then you know the difference between “who” and “whom.” Who is nominative (subject) and “whom” is accusative (direct object) or dative (indirect object). Bang.