In Her Place

Now that you all know who she is, we needn't say "Cassia" every time. That's the whole purpose of a pronoun: standing in for a noun once it's already known.

So a pronoun is a noun's understudy.

She sent the cassia. We ought to thank her for it.

Notice "she" did the sending, and "her" receives the thanks. Same person, two different jobs.

That's the whole system: "I, you, he, she, it, we, they" when the pronoun acts. "Me, you, him, her, it, us, them" when it's acted upon. English barely changes its nouns for this — but it never stops changing its pronouns.

Which is exactly why getting them backward sounds so wrong, even to an ear that couldn't explain the rule.

Is this her scroll-case, or is it hers?

Both, and neither is wrong — they only work differently.

"Her scroll-case" — "her" sits in front of the noun, holding its place, the way an adjective would. "It is hers" — "hers" stands completely alone. It doesn't need a noun following it at all; it's already doing the noun's job.

One borrows a noun's spot. The other replaces it outright.

She blames herself for the delay.

"Herself" there is the object of "blames" — the same person doing the blaming is the one being blamed. That's a true reflexive: the action bounces back onto its own subject.

She weighed it herself, before I ever touched the scale.

Here "herself" isn't the object of anything — "it" already is. This "herself" only insists that she, personally, did the weighing. Same word, a different job: emphasis, not reflection.

And when the action passes between two people, not back onto one: "Marcos and Demetria have been contradicting each other all morning."

Reflexive turns inward. Reciprocal turns toward someone else, and back again.

"This is the case she sent. That, apparently, is not."

You've pointed at two different things and used the same kind of word for both.

"This" and "these" point to what's near you. "That" and "those" point to what's farther off. All four can stand entirely alone, doing a noun's work without borrowing one.

A pronoun that points is still a pronoun. It just gestures instead of naming.

The messenger who arrived at dawn is still here.

"Who" there isn't asking a question. It's opening a clause and standing in for the messenger inside it — a relative pronoun.

Use "who" when your pronoun would be doing the action inside its own clause, and "whom" when it's on the receiving end: "the woman whom we thanked already left." "Whom" is fading from ordinary speech, but the distinction hasn't.

And "whose" does the same work as "her" or "his," except it can point back to a person you haven't named yet: "the scholar whose latch broke has been quiet all day."

And for things, not people?

"Which" and "that." "The parcel, which she sent, arrived damaged" — remove that clause and the sentence still stands. But "the parcel that arrived damaged" — pull the clause out of that one, and you no longer know which parcel you mean.

Someone left ink on the ledger again.

No one admits to it, either.

"Someone," "everybody," "nobody," "each" — every one of them sounds like it should take a plural verb, and every one of them takes a singular instead. "Everybody is here," never "are," however many bodies that happens to be.

An indefinite pronoun refuses to say how many. Grammar still insists on treating it as one.

So a single word can replace a name, an owner, a direction, a whole clause, or a crowd too vague to count.

Which is precisely why I'd rather you learned to use them properly than keep saying "Cassia" fourteen times in one sentence.