[Casiopea]

In addition,

[1] Descriptive grammar: a grammar that "describes" how language is used by its speakers.

For example,I am older than her.

Explanation: Subject pronouns (she, he, it, and so on) are paired with a verb, whereas object pronouns (her, him, it, and so on) are not. Since the phrase "than her" doesn't have a verb we can see or hear, some speakers choose an object pronoun in the context.

[2] Prescriptive grammar: a grammar that "prescibes" how speakers should use the language.

For example, I am older than she (is older).

Explanation: 'than' is a conjunction; it joins two like forms: "I am older" with "she is older", giving "I am older than she is older", but speakers omit the last part "is older" because it's redundant. Nevertheless, according to prescriptive grammar, 'than' functions as a conjunction, so speakers should use "she" in that context.